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PRINCETON,  N.  J. 


BL  175  .B88  1834 
Prout,  William,  1785-1850 
Chemistry,  meteorology,  and 
the  function  of  digestion 


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THE   BRIDGEWATER   TREATISES, 

ON  THE   POWER,   WISDOM,   AND   GOODNESS   OF  GOD,  AS 
MANIFESTED   IN   THE  CREATION. 


TREATISE  VIII. 

CHEMISTRY,  METEOROLOGY,  AND  THE  FUNCTION  OF  DIGESTION, 
^Y  WILLIAM  PROUT,  M.D.  F.R.S. 


OVK  aV  iJ'yvXTO    ^VVU/UiV    iTl   KXKZs   i^OVTA  Tot    iyKiK0(rfX3L/UiV*. 

HIPPODAMUS  DE  FELICITATE. 


CHEMISTRY,  METEOROLOGY, 


AND 


THE    FUNCTION    OF    DIGESTION 


CONSIDERED  WITH 


REFERENCE   TO  NATURAL   THEOLOGY. 


BY 


WILLIAM    PROUT,    M.D.  F.R.S 


FELLOW  OF  THE  ROYAL  COLLEGE  OF  PHYSICIANS. 


PHILADELPHIA: 
CAREY,     LEA    &     BLANCHaRD. 

1834. 


TO 


DAVIES    GILBERT,    ESQ. 


LATE  PRESIDENT  OF  THE  ROYAL  SOCIETY, 


^f^in  Volntat 


IS 


RESPECTFULLY  LVSCRIBED. 


NOTICE. 


The  series  of  Treatises,  of  which  the  present  is  one,  is  published 
under  the  followinir  circumstances  : 

The  Right  Honourable  and  Reverend  Francis  Henry,  Earl  of 
Bridgewater,  died  in  the  month  of  February,  1829;  and  by  his  last 
Will  and  Testament,  bearing  date  the  25th  of  February,  1825,  he  di- 
rected certain  Trustees  therein  named  to  invest  in  the  public  funds  the 
sum  of  Eight  thousand  pounds  sterling;  this  sum,  with  the  accruing 
dividends  ihereon,  to  be  held  at  the  disposal  of  the  President,  for  the 
time  being,  of  the  Royal  Society  of  London,  to  be  paid  to  the  person 
or  persons  nominated  by  him.  The  Testator  further  directed,  that  the 
person  or  persons  selected  by  the  said  President  should  be  appointed 
to  write,  print,  and  publish  one  thousand  copies  of  a  work  On  the 
Power,  fVisdom,  and  Goodness  of  God,  as  manifested  in  the  Creation; 
illustrating  such  work  by  all  reasonable  arguments,  as  for  instance  the  va- 
riety and  formation  of  God's  creatures  in  the  animal,  vegetable,  and  mi- 
neral kingdoms,-  the  effect  of  digestion,  and  thereby  of  conversion ,-  the 
construction  of  the  hand  of  man,  and  an  infinite  variety  of  other  arguments  ; 
as  also  by  discoveries  ancient  and  modern,  in  arts,  sciences,  and  the  whole 
extent  of  literature.  He  desired,  moreover,  that  the  profits  arising  from 
the  sale  of  the  works  so  published  should  be  paid  to  the  authors  of  the 
works. 

The  late  President  of  the  Royal  Society,  Davies  Gilbert,  Esq.  re- 
quested the  assistance  of  his  Grace  the  Archbishop  of  Canterbury  and 
of  the  Bishop  of  London,  in  determining  upon  the  best  mode  of  carry- 
ing into  effect  the  intentions  of  the  Testator.  Acting  with  tlieir  advice, 
and  with  the  concurrence  of  a  nobleman  immediately  connected  with 
the  deceased,  Mr.  Davies  Gilbert  appointed  the  following  eight  gentle- 
men to  write  separate  Treatises  on  the  different  branches  of  the  subject 
as  here  stated : 

THE  REV.  THOMAS  CHALMERS,  D.  D. 

Professor  of  Divinity  in  the  University  of  Edinburgh. 

ON  THE  POWER,  WISDOM,  AND    GOODNESS    OF    GOD    AS  MANIFESTED  IN  THE 

ADAPTATION  OF    EXTERNAL    NATURE    TO    THE    MORAL    AND 

INTELLECTUAL  CONSTITUTION  OF  MAN. 


JOHN  KIDD,  M.  D.  F.  R.  S. 

Regius  Professor  of  3Iedicine  in  the  University  of  Oxford. 

ON  THE  ADAPTATION  OF  EXTERNAL  NATURE  TO  THE  PHYSICAL  CONDITION 

OF  MAN. 
1* 


VI 


THE  REV.  WILLIAM  WHEWELL,  M.A.  F.R.S. 

Fellow  of  Trinity  College,  Cambridge. 

ASTRONOMY    AND    GENERAL    PHYSICS    CONSIDERED    WITH    REFERENCE    TO 

NATURAL  THEOLOGY. 


SIR  CHARLES  BELL,  K.  G.  H.  F.R.S.  L.&E. 

THE  HAND  :  ITS  MECHANISM  AND  VITAL  ENDOWMENTS  AS  EVINCING  DESIGN. 


PETER   MARK   ROGET,    M.  D. 

Fellow  of  and  Secretary  to  the  Royal  Society. 
ON  ANIMAL  AND  VEGETABLE  PHYSIOLOGY. 


THE  REV.  WILLIAM  BUCKLAND,  D.D.  F.R.S. 

Canon  of  Christ  Church,  and  Professor  of  Geology  in  the  University  of  Oxford. 
ON  GEOLOGY  AND  MINERALOGY. 


THE  REV.  WILLIAM  KIRBY,  M.A.  F.R.S. 

ON  THE  HISTORY,  HABITS,  AND  INSTINCTS  OF  ANIMALS. 


WILLIAM  PROUT,  M.D.  F.R.S. 

CKEMISTRY,  METEOROLOGY,  AND  THE  FUNCTION  OF  DIGESTION,  CONSIDERED 
WITH  REFERENCE  TO  NATURAL  THEOLOGY. 


His  Royal  Highness  the  Duke  of  Sussex,  President  of  the  Royal 
Society,  having-  desired  tiiat  no  unnecessary  delay  should  take  place  in 
the  publication  of  the  above  mentioned  treatises,  they  will  appear  at 
short  intervals,  as  they  are  ready  for  publication. 


TO    THE    READER. 


Chemistry  has  not  hitherto  been  considered  in  detail  with 
reference  to  Natural  Theology:  the  difficulties,  therefore, 
incidental  to  a  first  attempt,  added  to  those  arising  from  the 
nature  of  Chemistry  itself  as  a  science,  must  be  the  apology 
of  the  author  for  numerous  imperfections  in  this  treatise. 

The  peculiar  chemical  opinions  advanced,  would  never 
have  appeared  in  their  present  form ;  had  not  the  author 
been  strongly  impressed  with  the  belief  that  they  are  calcu- 
lated, sooner  or  later,  to  bring  chemical  action  under  the 
dominion  of  the  laws  of  quantity ;  and  had  he  not  despaired, 
under  his  professional  engagements,  of  being  himself  able  to 
submit  them  to  experimental  proof  These  opinions,  how- 
ever, have  been  always  introduced  as  mere  illustrations. 

The  argument  of  design  is  necessarily  cumulative ;  that 
is  to  say,  is  made  up  of  many  similar  arguments.  To  avoid 
repetitions  therefore,  the  illustration  of  principles  rather  than 
of  details,  has  been  studied ;  and  the  application  of  particular 
facts  to  the  argument,  has  been  often  left  to  the  Reader. 

LONDO?:, 

February  3,  1834. 


CONTENTS. 


iNTnoDtrcTioif. 


Of  the  Leading  Argument  of  Natural  Theology  ;  that  Design,  or  the 

Adaptation  of  Means  to  an  End  exists  in  Nature.  23 

BOOK  1. 

CHEMISTRY. 

Preliminary  Observations  on  the  Rank  of  Chemistry  as  a  Science  ; 
and  on  the  Apphcation  of  Chemistry  to  the  Argument  of  De- 
sign. 25 
Chapter  T. — Of  the  Mutual  Operation  of  Physical  Agents  and  of  Mat- 
ter, and  of  the  Laws  which  they  obey.  32 
Chapter  II. — Of  the  Inertia  and  Activity  of  Matter.  33 
Chapter  III. — Of  Molecular  or  Polarizing  Forces,  etc.  35 
Section  I.  Of  the  Divisibility  of  Matter.  35 
Section  II.  Of  the  Forms  of  Aggregation  of  the  ultimate  Mole- 
cules of  Matter.  o7 
Section  III.  Of  the  solid  Form  of  Bodies.     Crystallization.  38 
Of  Electricity.  42 
Of  Magnetism.  44 
Of  Polarity.  46 
Section  IV.   Of  the  Liquid  Form  of  Bodies.     Of  Heat.  48 
Of  the  Latency  of  Heat.  51 
Section  V.  Of  the  Gaseous  Form  of  Bodies.  53 
Of  the  Diffusion  of  Gaseous  Bodies.  55 
Of  the  equal  Expansion  of  Gaseous  Bodies  ;  and  of  their  simi- 
lar Capacit}^  for  Heat.  56 
Section  VT.  Of  the  other  Properties  of  Heat.    Of  Heat  in  Motion. 

Of  the  Radiation,  Conduction,  and  Convection  of  Heat.  57 
Section  VII.  Of  Light.  59 
Of  the  Radiation  of  Light.  59 
Of  the  Reflection  and  Refraction  of  Light.  .  60 
Of  the  Polarization  of  Light.  61 
Of  the  Decomposition  of  Light.  63 
Section  VIII.  Of  the  Sources  of  Heat  and  Light.  65 
Section  IX.  Recapitulation  and  General  Observations  on  the  Sub- 
jects treated  of  in  the  preceding  Chapters.  66 
Arguments  in  Proof  of  design,  Deducible  from  the  Divisibility 

and  Molecular  constitution  of  Matter  68 
Chapter  IV — Of  Chemical  Elementary  Principles,  and  of  the  Laws 

of  their  Combination.  71 

Section  I.  Of  Chemical  Elementary  Principles,             '  72 
Of  the  Five  Elementary  Supporters  of  Combustion  j  Oxygen, 

Chlorine,  Bromine,  Iodine,  and  Fluorine.  73 


X  CONTENTS. 

Of  Elements,  wliich  instead  of  Supporting-  Combustion,  are 

for  the  most  part  themselves  Combustible.  76 

Of  the  Eig-ht  Elements  not  Metallic,  generally  termed  Acidifia- 
ble  Bases,  most  of  which  are  Combustible  ;  Hydrog-en,  Car- 
bon, Azote,  Boron,  Silicon,  Phosphorus,  Sulphur,  Selenium     76 
Of  the  Ten  Metalloids,  Arsenic,  Antimony,  Tellurium,  Cliro- 
mium.  Uranium,  Vanadium,  Molybdaenum,  Tungsten,  Tita- 
nium, Columbium.  80 
Of  the  Twelve  Metallic  Bases  of  the  Alkalies  and  Earths  ;  Po- 
tassium,   Sodium,   Lithium,   Calcium,  Magnesium,  Stron- 
tium, Barium,  Aluminum,  Glucinum,  Yttrium,  Zirconium, 
and  Thorinum,  80 
Of  the  Nineteen  Metals  Proper  ;  Iron,  Manganese,  Nickel,  Co- 
balt,Cerium,  Zinc,  Cadmium,  Lead,Tin, Bismuth,  Copper, 
Mercury,   Silver,  Gold,  Platinum,   Palladium,  Rhodium, 
Iridium,  Osmium.                                                                             83 
Section- II.  Of  the  Laws  of  Chemical  Combination.                              86 
Of  the  Atomic  Theory.                                                                        93 
Of  the  Representation  of  the  Combining  Molecules  of  Bodies 

by  Numerical  series.  95 

Section  III.  General  Remarks  upon  Chemical  Compounds.  95 

Of  Primary  Compounds.  96 

Of  Acids.  96 

Of  Alkalies  and  Bases.  97 

Of  Neutral  Compounds.  98 

Of  Secondary  Compounds  ;  Salts.  98 

Section  IV.   Recapitulation.     General  reflections  on  the  Subjects 

treated  of  in  the  preceding  Chapters.  99 

Statement  of  the  P'acts  on  which  the  Atomic  Theory  is  Founded.     99 
Of  the  Adaptation  of  Subordinate  to  Primordial  Agents  and  Ele- 
ments, and  of  the  Means  by  which  these  Adaptations  have 
been  effected.  100 

Of  Adaptations  produced  by  adjustments  of  quality  and  quantity  103 
of  the  Tendency  in  Nature  to  a  state  of  Repose  or  Equilibrium  105 
Of  the  Creation  of  the  Elements  with  the  Properties  essential 

to  produce  perfect  Compounds.  108 

Of  the  wonderful  Nature  of  the  most  simple  Chemical  Processes     110 
Brief  Examination  of  certain  Objections  to  the  Argument  of  De- 
sign. Ill 

BOOK  II. 

Of   METEOnOLOGY  ;  COMPREHEKrniNG  A  GENERAL  SkETCII  OF  THE  CoX- 
STITUTION  OF  THE   GlOHE  ;  AND   OF  THE  DlSTRIlirTION  AND  MUTUAL 

Influence  of  the  Agents  and  elements  of  Chemistry  in  the 
Economy  of  Nature. 

Preliminary  Observations.  114 

Chapter  I — Of  the  General  Structui'e  of  the  Earth  ;  particularly 
with  reference  to  the  Distribution  of  its  Surface  into  Land  and 
Water  ;  and  witli  respect  to  its  Atmosphere.  115 

Section  I.  Of  the  General  Relations  of  the  Sea  and  Land  to  each 

other.      •  115 

Section  II.   Of  the  Ocean.  116 

Section  III.   Of  the  Atmosphere.  118 


CONTENTS.  XI 

Chapter  II. — Of  Heat  and  Light  :  the  Modes  of  Estimating-  their  De- 
gree, and  the  Ways  in  which  they  are  Propag'ated.    Of  the  Gene- 
ral Temperature  of  the  Celestial  Reg-ions,  and  of  the  Earth  inde- 
pendently of  the  Sun.  122 
Section  I.   Of  Heat  and  Lig-ht,  and  the  Modes  of  estimating'  their 

deg-ree.  122 

Section-  II.    Of  the  Propag-ation  of  Heat  and  Lig-ht.  123 

Section  III.   Of  the  Temperature  of  the  Celestial  Regions.  124 

Section-  IV.   Of  the  Temperature  of  tlie  Interior  of  the  Earth.  124 

Chapteu  III.    Of  the  Temperature  of  the  Earth  at  its  Surface,  as  de- 
pendent on  the  Sun.  127 
Section  I.   Of  Mean  Temperature.  128 
Section  II.  Of  tlie  actual  Distribution  of  Temperature  over  the 

Globe.      Of  Isothermal  Lines,  &.C.      Climate.  129 

Of  the  Temperature  of  the  Poles  and  of  the  Polar  Regions.     129 
Of  the  mean  annual  Temperature  of  the  Equator.  150 

Of  tlie   Temperature  of  the  intermediate   Regions  of  the 

Globe.     Of  Isothermal  Lines,  8<c.  130 

Climate.  134 

CtiAPTEn  IV. — Of  the  Primary  Constituents  of  Climate  :  or  of  the  Tem- 
perature of  the  Earth,  as  dependent  on  its  Globular  Form  •,  and 
on  its  Annual  and  Diurnal  Motions.  _.  134 

Chaptku  V.  Of  the  secondary  or  subsidiary  Constituents  of  Climate  ; 
comprehending  a  Sketch  of  those  Circumstances  capable  of  In- 
fluencing Climate,  which  are  the  more  immediately  connected 
^vith  the  Surface  of  the  Earth,  as  consisting  of  Land  or  Water  ; 
or  which  are  connected  with  the  Atmosphere.  136 

Section  I.  Of  the  secondary  Constituents  of  Climate,  Immediately 
connected  with  the  Surface  of  the  Earth;  and  depending-  on 
the  Nature  of  that  Surface  of  the  Earth  ;  and  depending  on  the 
Nature  of  that  Surface  as  composed  of  Land  or  Water.  137 

1.  Of  the  Proportion  of  Solar  Heat  and  Light  that  actually 
arrives  at  tlie  Surface  of  the  Earth.  137 

2.  Of  the  Distribution  of  Heat  and  Light  over  the  Earth's 
Surface  in  the  latent  and  Decomposed  Forms.  138 
Of  tlie  General  Distribution  of  Electricity  and  Magnetism 

over  the  Earth.  139 

Of  the   Distribution  of  Light  in  the  decomposed  Form 
over  the  Earth.  141 

3.  Of  the  Laws  of  Absorption,  Radiation,  and  Reflection  of 
Heat  and  Light.  142 

4.  Of  the  Conduction  of  Heat  below  the  Earth's  Sui'face  on 
Land.  145 

5.  Of  the  Propagation  of  Heat  and  Light  below  the  Earth's 
Surface  in  Water.  146 
Of  tlie  Temperature  of  the  Waters  of  the  Ocean  at  great 

Depths.  150 
Of  the  under  Currents  of  the  Ocean  existing  between  the 

Equatorial  and  the  Polar  Regions.  150 

Temperatiu-e  on  Land  and  at  Sea.  151 

Temperature  of  Natural  Springs.  152 
Section  II.   Of  the  Secondary  Constituents  of  Climate  immediately 

connected  with  the  Atmosphere.  153 
1.   Of  the  Distribution  of  heat  and  of  light  through  the  At- 
mosphere, and  of  the  Consequences.  153 


Xll  CONTENTS. 

Of  the  Limits  of  Perpetual  Snow.  154 

Of  the  Distribution  of  Heat  and  Light  through  the  Atmo- 
sphere in  their  Latent  and  Decomposed  Forms.  156 
Of  the  Propagation  of  Sensible  Heat  through  the  Atmo- 
sphere. 156 
Of  Atmospheric  Currents.     The  Trade  Winds.                    158 
2.   Of  the  Presence  of  Water  in  the  Atmosphere.                           160 
Of  the  Relations  of  the  Water  in  the  Atmosphere  to  Tem- 
perature. 160 
Of  the  General  Relations  of  Evaporation  and  Conden- 
sation.                                                                                      167 
Of  the  Actual  Quantity  of  Water  that  is  evaporated  and 

condensed  over  the  Eartli.  176 

Of  Dew  and  Hoar  Frost.  178 

Of  Mists  and  Fogs.  180 

Of  Clouds.  181 

Of  Snow  and  Sleet.  185 

Of  Rain.  186 

Of  Hail.  189 

Of  the  Distribution  of  Heat  and  Light  in  their  latent  and 
decomposed  Forms  througli  the  Vapour  of  the  Atmo- 
sphere ;  and  of  the  Effects  of  that  Distribution.  190 
Of  the  Relations  of  Electricity  to  the  Vapour  of  the  At- 
mosphere. 190 
Of  the  Aurora  Borealis.  192 
Of  the  Phenomena  depending  upon  the  Decomposition, 
Refraction,  and  Reflection  of  Light  by  the  Vapour  of 
the  Atmosphere.     The  Mirage.      The  Fata  Morgana. 
Halos.    The  Rainbow.                                                              192 
3.  Of  the   Occasional  Presence  of  Foreign  Bodies  in  the  Atmo- 
sphere ;  and  of  their  Effects.                                                   194 
Of  Matter  suspended  in  the  Atmosphere  in  a  state  of  Mix- 
ture. Coloured  Rain  and  Snow.    Aerolites.     Dr}'  Fogs.     194 
Of  Matters  v.'hich  pervade  the  Atmosphere  in  a  state  of  So- 
lution.    Malaria.                                                                         197 
Recapitulation.     The  Arrangements  of  Climate  demonstra- 
tive of  Design.                                                                               198 
Ckapter  VI. — Of  the  Adaptation  of  Organized  Beings  to  Climate  ; 
comprehending  a  General  Sketch  of  the  Distribution  of  Plants 
and  Animals  over  the  Earth,  and  of  the  Present  Position  and  Fu- 
ture Prospects  of  Man.                                                                             203 
Of  the  Formation  and  Ingredients  of  the  Soil.                               203 
Sf.ctiox  I.   Of  the  Distribution  of  Plants  over  the  Earth.                  204 

1.  Of  the  Differences  of  Vegetation,  as  Hable  to  be  influenced 

by  Soil,  and  by  other  minor  Local  Circumstances,  in  the 
same  Climate.  204 

2.  Of  the  Influence  of  Climate  on  Vegetation.      Distribution 

of  Plants.  206 

Profusion  of  Vegetable  Productions.  210 

Sectiox  II.  Of  the  Distribution  of  Animals  over  the  Eartli.  212 

1.  Of  the  Difterences  existing  among  Animals  in  similar  Cli- 

mates. 213 

2.  Of  the  Effects  of  Diversity  of  Climate  on  the  Distribution 

of  Animals.  215 

Migration  and  Hybernation.  220 

Coverings  of  Animals.  220 


CONTENTS.  Xlll 

Section  III.  Of  the  present  Position  and  future  Prospects  of  Man.  222 

BOOK  III. 

Of  the  Chemistrx  of  Organizatiok  :  PAnxrcuLAULT  of  the  Che- 
MiCAi,  Process  of  Digestion  :  and  of  the  suBSEauENT  Pro- 
cesses, BY  WHICH  various  AlIMENTART  SuBSTANCES  ARE  ASSIMI- 
LATED TO  AND   BECOME  COMPONENT  PaRTS  OF,   A  LiVING  BoDY.  228 

Chapter  I, — Of  the  Nature  and  Composition  of  Organized  Bodies  in 

general,  as  compared  with  Inorg-anic  Matter.  228 

1.  Of  Organic  Bodies  considered  as  Chemical  Compounds.        229 

Of  the  Chemical  Composition  of  Sugar,  Vinegar,  Starch, 
and  Wood.  232 

2.  Of  the  Cause  of  the  Differences  in  the  Sensible  Proper- 

ties of  Substances  nearly  allied  in  their  Chemical  Composi- 
tion. 233 
Of  the  Peculiarity  of  the  Composition  of  Organic  Sub- 
stances. 233 
Of  the  Nature  of  the  Agents  by  which  Organic  Substances 
are  Produced.                                                                          235 

3.  Of  the  Modes  of  Operation  of  Organic  Agents.  237 

Reflections  on  the  Mutual  Adaptation  of  the  Elements 
and  the  Agents  of  Organic  Nature.  241 

Chapter  II. — Of  the  Modes  of  Nutrition  ;  comprehending  a  Sketch 
of  the  Alimentary  Apparatus ;  and  of  Alimentary  Substances 
in  Plants  and  in  Animals.  243 

Section  I.   Of  the  Modes  of  the  Nutrition  of  Plants  ;  and  of  the  Na- 
ture of  those  Matters  by  wliich  their  Nutrition  is  effected.         243 
Section  II.  Of  the  Modes  of  Nutrition  in  Animals  ;  and  of  the  Ali- 
mentary Substances  by  which  they  are  nourished.  246 
1.  Of  the  Organs  of  Digestion  in  Animals.  247 
Of  the  mouth  and  its  Appendages.  247 
Of  the  Oesophagus, the  Stomach,  and  the  Intestinal  Canal.  249 
Of  the  Liver,  the  Pancreas,  and  the  Spleen.  253 
Of  the  Circulation  of  the  Blood,  and  of  the  Distribution 

of  the  Nerves  in  the  Organs  of  Digestion.  254 

Of  Alinientary  Substances  composed  of  the  Saccharine, 
the  Oily,  and  the  Albuminous  Principles.      ■  256 

Chapter  III. — Of  the  Digestive  Process  ;  and  of  the  General  Action 

of  the  Stomach  and  the  Duodenum.  261 

Of  the  Influence  of  Water  as  an  Essential,  and  as  an  Acci- 
dental Ingredient  of  Alimentary  Substances.  261 
Of  the  Powers  exerted  by  the  Stomach  in  the  Digestion  of 

the  Food.  265 

1.  Of  the  Reducing  Powers  of  the  Stomach.  265 

2.  Of  the  Powers  of  Conversion  possessed  by  the  Sto- 

mach. 269 

3.  Of  the  Organizing  and  Vitalizing  Powers  of  the  Sto- 

mach. 271 

Of  the  Changes  the  Food  undergoes  in  the   Duode- 
num, 721 
Of  the  Functions  of  the  Alimentary  Canal,  beyond  the 
Duodenum.  273 
Observations  on  tlie  Choice  and  the  Preparation  of  Aliment.  274 
Observations  on  the  General  Character  of  the  Assimilating 

Agency.  275 

2 


XIV  CONTENTS. 

Chapter  IV. — Of  the  Processes  of  Assimilation  subsequent  to  those  in 
the  Stomach  and  Alimentary  Canal ;  particularly  of  the  Conver- 
sion of  the  Chyle  into  Blood,  Of  Respiration  and  its  Uses.  Of 
the  Final  Decomposition  of  Organized  Bodies.  General  Reflec- 
tions and  Conclusion.  277 

1.  Of  the  Passage  of  the  Chyle  from  the  Alimentary  Canal 

into  the  Sanguiferous  System  ;  and  of  the  Function  of 
Absorption  generally.  277 

Process  similar  to  Digestion  carried  on  in  all  Parts  of  the 
Body.  279 

2.  Of  the  Blood.  279 

Of  the  Constituents  of  the  Blood.  279 

Of  the  Organization  of  the  Blood.  280 

3.  Of  Respiration.  280 

Of  the  different  Colours  of  Arterial  and  of  Venous  Blood.  282 
Of  tlie  Source  of  the  Carbonic  Acid  in  Venous  Blood,  and 
of  the  Gaseous  Vapour  that  is  expelled  from  tlie 
Lungs.  282 

Of  the  Use  of  the  continual  Extraction  of  Carbonic  Acid 

from  Living  Animals,  282 

4.  Of  Secretion.  283 

5.  Of  the  Spontaneous  Decay  of  Organized  Bodies.  284 
Recapitulation  of  the  Mechanical  Arrangements  of  the  Di- 
gestive Organs,  and  of  the  Chemical  Changes  by  which 
the  Food  is  adapted  for  Assimilation.  285 

Reflections  on  the  Mutual  Dependence  of  Plants  and  Ani- 
mals. On  the  Subserviency  of  their  Mechanism  to  the 
Chemical  Properties  of  Matter  ;  and  on  the  beneficial 
Effects  of  their  Renovation  and  Decay.  288 

Conclusion.  Of  the  Future  Progress  of  Chemistry  ;  of  the 
Application  of  Chemistry  to  Physiological  Research  ; 
and  of  the  Tendency  of  Physical  Knowledge  to  elevate 
the  Mind  by  Displaying  the  Attributes  of  the  Deity  and 
the  Immensity  of  His  Works.  291 

Appendix.— Contahnng  Additional  Notes  and  Emendations.  297 


INTRODUCTION. 


OF  THE  LEADING  ARGUMENT  OF  NATURAL  THEOLOGY;    THAT  DESIGN,  OR 
THE  ADAPTATION  OF  MEANS  TO  AN  END,  EXISTS  IN  NATURE. 

With  the  view  of  illustrating  the  argument  of  design,  we  shall 
commence  with  a  statement  of  that  argument  in  its  simplest  form. 

Animals  in  cold  climates  have  been  provided  with  a  covering 
of  fur.  Men  in  such  climates  cover  themselves  with  that  fur.  In 
both  cases,  whatever  may  have  been  the  end  or  object,  no  one 
can  deny  that  the  effect^  at  least,  is  precisely  the  same  :  the  ani- 
mal and  the  man  are  alike  protected  from  the  cold.  Now,  since 
the  animal  did  not  clothe  itself,  but  must  have  been  clothed  by 
another ;  it  follows,  that  whoever  clothed  the  animal,  must  have 
known  what  the  man  knows,  and  must  have  reasoned  like  the 
man  ;  that  is  to  say,  the  clother  of  the  animal  must  have  known 
that  the  climate  in  which  the  animal  is  placed,  is  a  cold  climate  ; 
and  that  a  covering  of  fur,  is  one  of  the  best  means  of  warding  off 
the  cold  ;  he  therefore  clothed  his  creature  in  this  very  appropriate 
material. 

The  man  who  clothes  himself  in  fur  to  keep  off  the  cold,  per- 
forms an  act  directed  to  a  certain  end  ;  in  short,  an  act  of  design. 
So,  whoever,  directly  or  indirectly,  caused  the  animal  to  be  clothed 
with  fur  to  keep  off  the  cold,  must  likewise  have  performed  an 
act  of  design. 

But,  under  the  circumstances,  the  clother  of  the  animal,  must 
be  admitted  to  have  been  also  the  Creator  of  the  animal ;  and  by 
extending  the  argument ;  the  Creator  of  man  himself — of  the  uni- 
verse. Moreover,  the  reasoning  the  Creator  has  displayed  in 
clothing  the  animal,  He  has  designed  to  impart  to  man,  who  is 
thus  enabled  to  recognize  his  Creator's  design. 

Such  is  an  instance  of  those  varied  adaptations  of  means  to  ends 
around  him,  which  man  by  his  reasoning,  appreciates  ;  and  which 
demonstrate  to  him,  the  existence  of  an  intelligent  Creator.  Com- 
pared, however,  with  the  extent  of  creation,  the  instances,  nu^ 


24  INTRODUCTION. 

merous  as  lliey  appear,  in  which  man  is  thus  able  to  trace  the 
designs  of  his  Creator,  are  really  few.  Man  not  only  sees  means 
directed  to  certain  ends  ;  but  ends  accomplished  by  means,  which 
he  is  totally  unable  to  understand.  He  also  sees,  every  where, 
things,  the  nature,  and  the  end  of  which  are  utterly  beyond  his 
comprehension;  and  respecting  which,  he  is  obliged  to  content 
himself  with  simply  inferring  the  existence  of  design. 

The  argument  of  design,  therefore,  in  its  general  sense,  em- 
braces at  least  three  classes  of  objects  : — 

1.  Those  objects,  regarding  which,  the  reasoning  of  man  coin- 
cides with  the  reasoning  evinced  by  his  Creator  ;  as  in  the  sim- 
ple adaptation  of  clothing  above  mentioned :  or  those  objects,  in 
which,  man  is  able  to  trace,  to  a  certain  extent,  his  Creator's  de- 
signs ;  as  in  various  phenomena  amenable  to  the  laws  of  quantity ; 
viz.  mechanics,  &:c. 

2.  Those  objects,  in  which,  man  sees  no  more  than  the  pre- 
liminaries and  the  results,  or  the  end  and  design  accomplished  ; 
without  being  able  to  trace  through  their  details,  the  means  of  that 
accomplishment ;  as  in  all  the  phenomena  and  operations  of 
chemistry. 

3.  Those  objects,  in  which,  design  is  inferred,  but  in  which 
the  design,  as  well  as  the  means  by  which  it  is  accomplished,  are 
alike  concealed ;  as  in  the  existence  of  fixed  stars,  of  comets,  of 
organized  life  ;  and  indeed  in  all  the  great  and  more  recondite 
phenomena  of  nature. 

The  intention  of  these  Treatises,  is  to  point  out  the  various  evi- 
dences of  design,  among  the  objects  of  creation  ;  and  to  deduce 
from  them,  the  existence,  and  the  attributes,  of  the  Creator.  The 
following  pages  are  occupied  more  particularly,  with  the  illustra- 
tion of  the  evidences  of  design,  in  objects  belonging  to  the  second 
of  the  three  classes  above  mentioned ;  with  those,  namely,  in 
which  design  is  obvious,  though  we  cannot  trace  the  means  by 
which  that  design  is  accomplished. 


BOOK  I. 


OF    CHEMISTRY. 


PRELIMINARY  OBSERVATIONS  ON  THE  RANK  OF  CHEMISTRY  AS  A  SCIENCE; 
AND  ON  ITS  APPLICATION  TO  THE  ARGUMENT  OF  DESIGN. 

"  Chemistry  does  not  afford  the  same  species  of  argument  (in 
favour  of  design)  that  mechanism  affords,  and  yet  may  afford  an 
argument  in  a  high  degree  satisfactory."  *  This  remark  of  the 
excellent  Paley  has  been  made  by  him  with  reference  only  to  a 
particular  subject,  but  the  following  sketch,  pointing  out  the 
grounds  upon  which  chemistry  as  a  science  is  foundei!,  and  the 
rank  which  it  holds  among  the  departments  of  human  knowledge, 
will  at  the  same  time  show  the  general  truth  of  the  remark. 

An  elaborate  inquiry  into  the  origin  and  nature  of  human  know- 
ledge would  be  quite  misplaced  here.  We  shall  content  ourselves 
with  simply  considering  it  as  of  two  kinds,  viz  :  a  knowledge  of 
what  must  be  ;  that  is  to  say  of  what  we  cannot  conceive  eitiier 
not  to  exist,  or  to  exist  otherwise  than  as  it  is,  and  which  is  there- 
fore founded  upon  reason  ;  and  a  knowledge  of  what  simply  is, 
but  how  or  why  we  know  not,  and  for  the  existence  of  which, 
therefore,  we  can  assign  no  reason  but  our  experience  alone. 

Of  these,  the  only  instance  of  the  first  kind  which  particularly 
concerns  us  at  present,  is  the  knowledge  of  quantity  and  its  rela- 
tions in  general;  of  the  second,  that  of  certain  natural  phenomena, 
the  consideration  of  which  constitutes  the  principal  object  of  the 
present  volume. 

The  fundamental  differences  between  these  two  great  branches 
of  human  knowledge,  as  well  as  their  consequences,  cannot  per- 
haps be  more  strikingly  illustrated  than  in  the  following  familiar 
exposition  by  a  celebrated  writer.  "  A  clever  man,"  says  Sir  J. 
Herschel,  "shut  up  alone  and  allowed  unlimited  time,  might 
reason  out  for  himself  all  the  truths  of  mathematics,  by  proceed- 
ing from  those  simple  notions  of  space  and  number  of  which  he 
cannot  divest  himself  without  ceasing  to  think ;  but  he  would  never 
tell  by  any  effort  of  reasoning  what  would  become  of  a  lump  of 
sugar,  if  immersed  in  water,  or  what  impression  would  be  pro- 

*  Natural  Theolog-y,  chap.  vii. 
3 


26  INTRODUCTION. 

duced  on  his  eye  by  mixing  the  colours  yellow  and  blue,"*  results 
which  can  be  learnt  only  from  experience. 

Thus  then  the  extremes  of  human  kno\vledo;e  mav  be  considered 
as  founded  on  the  one  hand  purely  upon  reason,  and  on  the  other 
purely  upon  sense.  Now,  a  very  large  portion  of  our  knowledge, 
and  what  in  fact  may  be  considered  as  the  most  important  part  of 
it,  lies  between  these  two  extremes,  and  results  from  a  union  or 
mixture  of  them,  that  is  to  say,  consists  of  the  application  of  ra- 
tional principles  to  the  phenomena  presented  by  the  objects  of 
nature. 

With  respect  to  knowledge  founded  upon  reason.^  we  are  so 
constituted,  that  whether  we  contemplate  those  primary  notions 
of  space,  time,  force,  &c.  above  alluded  to  in  the  abstract,  or 
whether  we  view  them  in  connexion  v/ith  the  objects  of  sense 
around  us,  we  cannot  divest  them  of  quantity,  which  seems  to 
be  involved  in  their  very  essence.  Quantity  and  its  relations, 
therefore,  in  some  shape  or  other,  enter  as  a  necessary  element 
into  by  fiir  the  greater  portion  of  humrai  knowledge.  Now  the 
primary  relations  of  quantity  are  exceedingly  simple  ;  one  quantity 
may  be  equal  to  anothef,  or  it  may  be  greater  or  less,  but  we  can 
conceive  no  other  relation.  Hence  all  the  operations  of  the  ma- 
thematics— the  science  of  quantity  and  its  relations — however 
abstruse  and  complicated  they  appear,  can  be  ultimately  resolved 
into  addition  and  subtraction. 

It  is  principally  then  through  the  medium  of  the  relations  of 
quantity  that  we  are  enabled  to  reason  in  a  satisfactory  manner 
upon  the  objects  of  sense.  For  as  everything  in  nature,  or  what 
is  the  same  thing  to  us,  every  sensation  produced  by  one  natural 
object,  as  compared  with  that  produced  by  another,  must  be  either 
equal  or  similar,  or  unequal  or  dissimilar ;  the  whole  are  capable 
of  being  subjected,  more  or  less  perfectly,  to  the  laws  of  quantity. 
This  is  effected  in  various  ways  and  by  various  artifices,  but 
chiefly  through  the  intervention  of  certain  natural  or  assumed 
units,  or  standards  of  resemblance,  as  a  second  in  time,  a  foot  in 
space,  &LC.,  and  in  proportion  to  the  definite  character  of  these 
units,  or  standards,  and  as  they  can  be  more  or  less  satisfactorily 
applied,  so  will  the  resulting  branch  of  knowledge  be  more  or  less 
of  a  mathematical  character,  or  be  more  or  less  rational  and  per- 
fect. 

By  contemplating,  in  the  abstract,  the  boundless  relations  of 
time  and  of  space,  where  no  end  can  be  conceived  to  addition  and 
subtraction,  we  arrive  at  the  only  notions  of  infinity  of  which  our 
nature  seems  capable.     These  once  obtained,  the  obvious  and  ne- 

*  Discourse  on  the  Study  of  Natural  Philosophy,  p.  76, 


INTRODUCTION.  27 

cessary  existence  of  cause  within  the  narrow  sphere  of  our  ob- 
servation naturally  leads  us  to  inquire,  can  this  cause  be  infinite  ? 
And  thus  we  are  led  by  degrees,  but  irresistibly,  to  the  sublimest 
of  all  conclusions,  that  a  Cause  or  Agent  in  every  way  commen- 
surate with  infinity — omniscient  and  omnipresent,  eternal  and 
omnipotent  must  exist — in  other  words,  a  God. 

Compared  with  infinity,  however,  and  even  with  the  objects  of 
nature  as  they  visibly  exist  around  us,  our  actual  knowledge  of 
time  and  of  space  is  exceedingly  limited.  Like  travellers  on  an 
extended  plain,  we  see  what  is  going  on  around  us  at  the  present 
moment,  but  the  distant  and  the  very  near,  the  past  and  the  future, 
are  alike  unknown  to  us.  A  few  millions  of  miles,  for  example, 
or  a  few  thousand  years,  comprise  the  utmost  that  we  know  of 
space  and  of  time.  On  the  other  hand,  beyond  the  fraction  of  an 
inch,  or  of  a  second,  everything  belonging  to  space  and  to  time  is 
inappreciable  by  our  senses.  Yet  beyond  these  limits  w^e  know 
that  myriads  of  portions  of  space  and  of  time  must  exist,  too  vast 
or  too  minute  to  be  referred  to  our  imperfect  standards.  Let  us, 
for  instance,  take  the  distance  of  the  nearest  fixed  star.  This  we 
are  assured  by  astronomers  is  so  great  that  the  utmost  measure 
we  can  apply  to  it — the  diameter  of  the  earth's  orbit — a  space  of 
no  less  than  192,000,000  of  miles  is  absolutely  too  little  to  measure 
it  by — is  in  fact  contained  within  it  so  many  times  that  the  num- 
ber cannot  at  present  be  counted  !  On  the  other  hand,  we  shall 
presently  find,  that  the  molecules  of  matter  of  which  the  objects 
we  see  around  us  are  composed  are  so  minute,  that  a  measure 
scarcely  appreciable  by  the  unassisted  sight,  the  thousandth  part 
of  an  inch  for  example,  is  vastly  too  large  to  compare  them  with, 
and  may  in  fact  comprise  millions  of  them  ! 

Experience,  the  great  and  ultimate  source  of  all  the  knowledge 
we  possess  of  those  portions  of  nature  to  which  our  faculties  are 
limited  may  be  acquired  in  two  ways  ;  by  simple  observation, 
and  by  experiment ;  that  is  to  say,  either  "  by  noticing  facts  as 
they  occur  without  any  attempt  to  influence  the  frequency  of  their 
occurrence,  or  to  vary  the  circumstances  under  which  they  oc- 
cur ;"  or  "  by  putting  in  action  causes  and  agents  over  which  we 
have  control,  and  purposely  varying  these  combinations,  and  no- 
ticing what  efTects  take  place."*  Now  in  all  the  higher  depart- 
ments of  knowledge  the  objects  of  which  are  principally  matter, 
and  its  motions  in  the  aggregate,  the  information  we  can  acquire 
by  one  or  both  these  means  is  so  complete,  and  at  the  same  time 
so  favourable  to  the  application  of  the  relations  of  quantitj^  that 
the  resulting  sciences  have  all  the  certainty  of  abstract  truths 

*  Herschel*s  Discourse  on  the  Study  of  Natural  Philosophy,  p.  76. 


38  INTRODUCTION, 

themselves.  But  when  the  knowledge  we  possess  of  objects  is 
wholly  sensible,  and  in  no  way  commensurate,  or  only  very  im- 
perfectly so  with  their  quantity,  here  it  is  that  uncertainty  begins  ; 
for  though  we  may  be  able  to  trace  the  apparent  cause  and  eff'ect 
of  a  particular  phenomenon,  the  most  minute  and  careful  obser- 
vation and  experiment,  often  give  us  but  little  insight  into  the 
connexion  between  the  two,  and  generally  fail  us  altogether.  The 
reason  of  this  is  to  be  sought  for  in  the  limited  nature  of  our  fa- 
culties, and  particularly  in  our  complete  ignorance  of  the  nature 
of  that  mysterious  communication  wliich  we  maintain  with  the 
external  world  through  the  medium  of  sensation.  In  two  of  the 
senses  indeed,  seeing  and  hearing,  we  are  able  to  trace  the  inter- 
mediate train  of  phenomena  between  the  external  object  producing 
the  sensation  and  the  sensation  itself,  and  even  to  form  some  idea  of 
the  remote  cause  of  the  sensation  ;  but  in  the  other  tv/o  senses, 
tasting  and  smelling,  the  whole  is  involved  in  mystery  from  be- 
ginning to  end. 

Thus  w^hen  a  bell  is  struck,  philosophers  have  satisfactorily 
demonstrated  that  a  vibratory  motion,  excited  in  the  bell,  and  de- 
pending upon  its  elasticity,  is  communicated  to  the  air  in  contact 
with  it,  and  through  this  medium  is  propagated  to  the  ear,  in  which 
organ,  we  know  not  why,  the  sensation  of  sound  is  excited.  Cir- 
cumstances very  similar  have  been  supposed  to  take  place  with 
respect  to  light,  and  undulse  (or  something  obeying  the  laws  of 
undidse)  have  been  demonstrated  to  exist  and  to  be  propagated 
from  the  luminous  body  to  the  eye,  and  thus  the  remote  cause  of 
sound,  and  probably  of  light,  is  proved  to  be  motion.  But  in  the 
cases  of  tasting  and  smelling  the  circumstances  are  altogether 
dissimilar  ;  here  the  sapid  and  odoriferous  matters  are  brought  at 
once  into  actual  contact  with  the  sentient  organs,  and  the  sensa- 
tions are  the  consequence  \vithout  any  intermediate  train  of  pheno- 
mena, at  least  any  that  we  can  appreciate.  What  it  is  therefore 
in  an  acid  or  a  rose  for  example,  analogous  to  motion  in  the  bell, 
and  which  produces  the  sensations  we  call  sour  and  siveet  we 
know  not,  and  probably  never  shall  know,  and  simply  because 
the  laws  and  relations  of  quantity  are  here  either  totally  inappli- 
cable, or  can  be  only  indirectly  and  most  imperfectly  applied. 

These  observations  are  principally  introduced  with  reference  to 
the  department  of  knowledge  we  have  at  present  to  consider.  Al- 
most all  of  M'hatare  denominated  the  chemical  properties  of  bodies, 
are  objects  of  taste  and  of  smell,  rather  than  of  sight  and  of  hear- 
ing. Hence  they  admit  only  of  the  indirect  application  of  the 
laws  of  quantity,  and  are  the  result,  not  of  reason  but  solely  of 
experience.  Indeed,  so  much  is  chemistry  the  creature  of  actual 
experimental  research,  that  its  simplest  truths  have  seldom,  been 


INTRODUCTION.  29 

anticipated  a  priori.  Thousands  of  years  of  observation  and  ex- 
perience for  example  had  not  taught  mankind  that  water  is  com- 
posed of  two  elementary  gaseous  principles,  much  less  the  pro- 
portions in  which  those  principals  combine  to  form  water. 
Nay,  even  now  the  fact  has  been  established  upon  the  clearest 
evidence,  we  are  unable  to  explain  why  it  is  so,  or  even  to  com- 
prehend the  nature  of  the  union  or  its  result.  Hence,  to  use  the 
language  of  Paley,  in  all  chemical  operations — "  our  situation  is 
precisely  like  that  of  an  unmechanical  looker-on,  Avho  stands  by 
a  machine,  the  fabric  of  which  is  hidden  from  his  sight  by  the 
outside  case,  or  if  seen,  would  be  too  complicated  for  his  unin- 
formed understanding  to  comprehend.  And  what,"  continues 
this  energetic  writer,  "  is  that  situation  ?  Ignorant  as  he  is,  he 
does  not  fail  to  see  that  certain  materials,  in  passing  through  the 
machine,  undergo  remarkable  changes  ;  and  what  is  more,  changes 
manifestly  adapted  for  future  use.  Is  it  necessary  that  this  man, 
in  order  to  be  convinced  that  design,  that  intention,  that  contri- 
vance, have  been  employed  about  the  machine,  should  be  allowed 
to  pull  it  to  pieces  to  study  its  construction  ?  He  may  indeed 
wish  to  do  this  for  many  reasons,  but  for  all  the  purposes  of  as- 
certaining the  existence  of  counsel  and  design  in  the  formation  of 
the  machine,  he  wants  no  such  intromission  or  privity.  What 
he  sees  is  sufficient.  The  effect  upon  the  material,  the  change 
produced  in  it,  the  utility  of  that  change  for  farther  applications 
abundantly  testify,  be  the  concealed  part  of  the  machine,  or  of  its 
construction  what  it  will,  the  hand  and  agency  of  a  contriver."* 

We  have  thus  attempted  to  point  out  the  rank  which  chemistry 
holds  among  human  knowledge,  and  the  kind  of  evidence  which 
it  furnishes  in  favour  of  design  ;  and  the  whole  argument  may  be 
briefly  recapitulated  as  follows  :  chemistry  is  a  branch  of  know- 
ledge founded  solely  on  experience,  for  the  phenomena  of  which 
we  can  assign  no  reason.  i3ut  although  the  intimate  nature  of  its 
changes  be  unknown  to  us,  we  see  them  manifestly  directed  to 
certain  ends  ;  hence  as  objects  directed  to  certain  ends,  where  the 
whole  of  the  intermediate  phenomena  can  be  traced  and  understood, 
always  imply  design,  we  naturally  infer  design  in  others  obvious- 
ly so  directed,  even  although  we  may  not  be  able  to  understand 
their  intimate  nature. 

Such  is  the  state  in  which  Paley  has  left  the  argument,  and 
while  we  admit  that  even  in  its  most  perfect  form,  it  is  less  sa- 
tisfactory than  that  founded  upon  mechanism,  we  have  always 
thought  that  our  excellent  author  has  not  made  quite  so  much  of 
his  subject  as  he  might  have  done,  and  that  the  very  imperfections 

*  Natural  Theology,  chap.  vii.  condensed  slig-htly,  but  the  argument 
strictly  adhered  to. 

3* 


30  INTRODUCTION. 

and  difficulties  of  chemistry  and  of  the  allied  branches  of  know- 
ledge give  them  some  advantages  over  mechanism  itself.  When 
a  series  of  wheels  or  of  levers  are  arranged  in  a  certain  order,  they 
must  move  in  a  certain  way,  and  produce  a  certain  effect  which 
can  be  foretold  exactly.  In  such  a  case,  we  may  admire  the  skill 
and  ingenuity  of  the  Contriver,  or  perhaps  feel  astonished  at  his 
power,  but  we  scarcely  do  more,  and  much  of  the  effect  is  lost  in 
the  apparent  necessity  of  the  result,  and  the  consciousness  that 
under  the  circumstances  nothing  else  could  have  happened.  When 
the  Deity,  therefore,  operates  through  the  medium  of  mechanism, 
he  appears  almost  too  obviously  to  limit  his  powers  within  the 
trammels  of  necessity ;  but  when  he  operates  through  the  me- 
dium of  chemistry,  the  laws  of  which  are  less  obvious,  and  indeed 
for  the  most  part  unknown  to  us,  his  operations  have  much  more 
the  character  of  those  of  a  free  agent,  and,  in  many  instances  also, 
appear  of  a  higher  order,  and  are  more  striking  and  wonderful. 
Do  not,  for  instance,  those  extraordinary  and  mysterious  changes 
constantly  going  on  around  us,  beneath  us,  within  us,  derive  no 
small  additional  interest  from  the  very  circumstance  of  their  not 
being  understood  ?  Just  such  an  interest,  to  revert  to  the  argument 
of  Paley,  as  the  unmechanical  looker-on  feels  in  the  operations 
of  a  corn-mill,  a  carding-machine,  or  a  threshing  machine,  and 
to  which  he  who  is  well  acquainted  with  the  mechanism  is  a 
stranger.  Certainly  this  is  the  case.  Obvious  mechanism,  though 
well  suited  to  display  the  intelligence  and  design  of  the  Contriver, 
is  not  always  so  well  adapted  for  arresting  the  attention  of  the  ob- 
server ;  its  very  obviousness  in  some  measure  depriving  it  of  its 
interest.  But  when  we  see  the  same  Contriver,  besides  the  most 
beautiful  and  complicated  mechanism,  employ  other  means  utterly 
above  our  comprehension,  though  evidently  most  familiar  to  hhn^ 
the  circumstance  is  not  only  calculated  to  arrest  our  attention  more 
forcibly,  but  at  the  same  time  to  impress  us  with  more  exalted 
notions  of  his  wisdom  and  power. 

There  yet  remain  one  or  two  other  points  to  be  briefly  consi- 
dered before  we  proceed  to  our  subject.  In  the  first  place  it  may 
be  asked,  do  those  extraordinary  changes  which  appear  to  be 
constantly  going  on  in  bodies  around  us,  indicate  real  and  sub- 
stantial changes  in  the  bodies  themselves,  or  are  they  mere  phan- 
tasms and  creations  of  the  organs  of  sense,  through  which  we  be- 
come acquainted  with  them?  The  discussion  of  this  question 
will  probably  be  considered  by  most  as  superfluous,  but  for  the 
sake  of  those  (if  there  be  any)  who  entertain  doubts  upon  the 
point,  it  may  be  remarked,  that  the  sensations,  though  admitted 
to  be  mere  signals  or  indications,  bearing  little  or  no  analogy  with 
the  causes  producing  them,  and  therefore  throwing  little  light  up- 


INTRODUCTION.  31 

on  their  nature,  do  nevertheless  represent  real  and  substantial  ope- 
rations of  some  sort  in  the  bodies  themselves.  This  miffht  be 
proved  were  it  necessary  by  a  variety  of  arguments,  but  one  or 
two  only  will  be  sufficient  for  our  present  purpose.  In  the  first 
place  it  may  be  stated,  that  changes  in  the  chemical  constitution 
of  bodies  are  usually  accompanied  by  corresponding  changes  in 
weight.  Now  weight  is  a  modification  oi  force ^  one  of  those 
self-evident  existences  which  we  cannot  doubt  without  doubting 
our  own.  Another,  and  perhaps  indeed  the  most  striking  argu- 
ment in  favour  of  the  reality  of  chemical  changes,  may  be  de- 
duced from  the  subserviency  to  them  of  those  mechanical  contri- 
vances and  operations  everywhere  existing  in  organized^  beings. 
At  least,  half  the  mechanism  in  a  living  animal  is  subservient  to 
the  chemical  changes  constantly  going  on  in  it,  and  necessary  to 
its  existence.  Take,  for  instance,  the  circulation  of  the  blood  : 
what  a  complicated  apparatus  is  here  employed  for  the  simple 
purpose  of  exposing  the  blood  to  the  action  of  the  air  in  the  lungs, 
in  order  that  it  may  there  undergo  some  chemical  change.  Now, 
surely  no  one  can  reasonably  doubt  that  this  chemical  change  is 
as  much  a  reality  as  the  mechanism  by  which  it  has  been  accom- 
plished ;  and  if  one  chemical  change  be  admitted  to  be  a  reality, 
why  may  not  all  others  ? 

Lastly,  if  there  be  any  one  who  denies  the  existence  of  design, 
and  sees  nothing  in  all  the  more  obvious  arrangements  and  order 
around  him  but  the  necessary  results  of  what  he  chooses  to  de- 
nominate "  the  laws  of  nature,"  let  him  calmly  and  deliberately 
consider  the  facts  brought  forward  in  the  following  pages  ;  and  if 
he  can  witness  unconvinced  all  the  numerous  instances  of  pro- 
spective arrangement  obviously  made  with  reference  to  things 
not  yet  in  existence  ;  all  the  beautiful  adjustments  and  adapta- 
tions of  noxious  and  conflicting  elements  most  wonderfully  con- 
spiring together  for  good  ;  and,  lastly,  the  subversion  of  even  his 
favourite  "  laws  of  nature"  themselves,  when  a  particidar  purpose 
requires  it ;  if,  we  say,  he  can  witness  all  these  and  still  remain 
incredulous  of  the  evidences  of  design,  we  can  only  observe, 
that  his  mind  must  be  most  singularly  constituted,  and  appa- 
rently beyond  the  reach  of  conviction. 


32  CHEMISTRY. 


CHAPTER  I. 

OF  THE  MUTUAL  OPERATION  OF  PHYSICAL  AGENTS  AND  OF  MATTER,  AND 

OF  THE  LAWS  WHICH  THEY  OBEY. 

"  God  has  been  pleased  to  prescribe  limits  to  his  own  power, 
and  to  work  his  ends  within  those  limits.  The  general  laws  of 
matter  have  perhaps  the  nature  of  these  limits  ;  its  inertia,  its  re- 
action, the  laws  which  govern  the  communication  of  motion,  of 
light,  of  heat,  of  magnetism  and  electricity,  and  probably  of 
others  yet  undiscovered.  These  are  general  laws,  and  when  a 
particular  purpose  is  to  be  effected,  it  is  not  by  making  them 
wind  and  bend  and  yield  to  the  occasion,  (for  nature  with  great 
steadiness  adheres  to  and  supports  them,)  but  it  is,  as  we  have 
seen  in  the  eye,  by  the  interposition  of  an  apparatus  correspond- 
ing with  these  laws,  and  suited  to  the  exigency  which  results 
from  them,  that  the  purpose  is  at  length  attained.  As  we  have 
said,  therefore,  God  prescribes  limits  to  his  power,  that  he  may 
let  in  the  exercise,  and  thereby  exhibit  demonstrations  of  his  wis- 
dom. For  then,  i.  e.  such  laws  and  limitations  being  laid  down, 
it  is  as  though  one  Being  should  have  fixed  certain  rules  ;  and, 
if  we  may  so  speak,  provided  certain  materials  ;  and  afterwards 
have  committed  to  another  Being,  out  of  these  materials,  and 
in  subordination  to  these  rules,  the  task  of  drawing  forth  a  crea- 
tion :  a  supposition  which  evidently  leaves  room,  and  induces 
indeed  a  necessity  for  contrivance.  Nay,  there  may  be  many 
such  agents,  and  many  ranks  of  these."*  This  admirable  pas- 
sage from  Paley  is  so  much  in  point,  and  so  exactly  expresses 
our  views  upon  the  subject,  that  we  have  chosen  it  as  a  text,  as 
in  a  former  instance,  for  illustration.  We  shall  proceed,  there- 
fore, to  take  a  summary  view  of  "  the  limits  within  w'hicli  the 
Deity  has  confined  his  operations  ;"  that  is  to  say,  of  the  laws 
by  which  matter,  and  these  subordinate  agents  by  which  it  is 
capable  of  being  influenced,  have  been  made  to  mutually  act  and 
react  upon  each  other. 

The  principles  of  activity  which  operate  as  subordinate  agen- 
cies in  nature  may  be  considered  as  of  two  kinds  ;  those  which 
operate  universally  upon  every  individual  atom  of  matter  without 
reference  to  its  sensible  properties,  as  the  forces  producing  the 
phenomena  of  gravitation,  &lc.  ;  and  those  which  operate  among 
the  different  constituent  molecules  of  which  all  bodies  are  com- 
posed, and  which  are  denominated  molecular  or  polarizing 
forces,  Slc.  Of  each  of  these  we  siiajl  in  the  first  place  endeavour 
to  convey  some  idea  to  the  general  reader. 

•  Nuturtil  Theology,    chap.  iii. 


INERTIA  AND  ACTIVITY  OF  MATTER.  33 


CHAPTER  IL 

ON  THE  INERTIA  AND  ACTIVITY  OE  MATTER. 

To  form  a  notion  of  what  is  termed  the  inertia  or  inactivity 
of  matter,  let  us  imagine  a  portion  of  it,  as  for  example,  a  ball  of 
lead  A  detached  from  all  other  matter,  and  existing  absolutely  un- 
influenced in  space.  Such  a  mass  of  matter,  if  supposed  to  be  at 
rest,  must  obviously  remain  so,  for  it  cannot  move  itself;  on  the 
other  hand,  if  it  be  supposed  to  be  in  motion,  it  must  continue  in 
motion,  for  it  cannot  be  conceived  to  be  able  to  stop  itself  any 
more  than  it  could  be  conceived  to  be  able  to  set  itself  in 
motion  ;  in  short,  a  mass  of  matter  under  such  circumstances  of 
isolation  must  be  considered  as  perfectly  passive  and  unable  to 
change  its  state,  whatever  that  may  happen  to  be,  whether  of 
motion  or- of  rest.  Now  let  us  suppose  another  portion  of  mat- 
ter, as  for  example,  another  ball  of  lead  b  exactly  of  the  same  size 
as  A,  placed  in  free  space  at  any  moderate  distance  from  a,  and 
away  from  all  other  influences,  \vhat  will  happen  ?  We  know 
from  general  experience  that  under  these  circumstances,  the  two 
balls  will  mutually  approach  each  other  with  an  accelerated  mo- 
tion, till  they  meet  at  a  point  exactly  intermediate  from  those  at 
which  they  first  started;  and  the  inference  from  this  experience 
is,  that  the  two  balls  exert  a  mutual  and  equal  attractive  force, 
which  causes  them  to  move  towards  each  other.  If  the  ball  b  be 
twice  the  size  of  the  ball  a,  the  two  balls  will  mutually  approach 
each  other  as  before,  but,  in  this  instance,  instead  of  moving  with 
equal  velocity,  while  the  ball  a  moves  two  feet,  the  ball  b  will 
only  move  one  foot ;  or  taking  an  extreme  case,  and  supposing 
the  ball  b  to  be  indefinitely  larger,  say  a  million  times  larger,  than 
the  ball  a,  they  will  mutually  influence  and  mutually  move  to- 
wards each  other  as  before,  but  the  motion  of  the  ball  b  will  be 
so  minute  as  to  be  insensible,  while  that  of  the  ball  a  will  be  the 
greatest  possible.  Here  we  have  instances  of  the  inertia  (inacti- 
vity, opposing  force,  &c.)  and  of  the  activity  (force  of  attraction, 
force  of  gravitation,  &c.)  which  all  matter  exerts  reciprocally  and 
mutually  towards  all  other  m.atter,  and  the  laws  of  which,  as  de- 
ducible  from  the  circumstances  stated,  and  from  others,  which  it 
would  be  foreign  to  our  present  purpose  to  enter  upon,  may,  in 
general  terms,  be  given  as  follows  :  "  The  mutual  attraction  of 
two  bodies  increases  in  the  same  proportion  as  their  masses  are 
increased,  and  as  the  square  of  their  distance  is  decreased,  and  it 
decreases  in  proportion  as  their  masses  are  decreased  and  as  the 


34  CHEMISTRY. 

square  of  their  distance  is  increased."  These  laws,  and  those  of 
the  motions  connected  with  them,  are  absolutely  general,  and  not 
only  extend  to  tlie  utmost  limits  of  the  universe  hitherto  explored 
by  man,  but  to  every  form  and  condition  of  matter,  without  ex- 
ception and  without  reference  to  its  other  properties.  They, 
therefore,  constitute,  probably,  the  most  comprehensive  "  limits 
which  the  Deity  has  been  pleased  to  prescribe  to  His  power," 
and  within  which  He  operates  with  the  most  unceasing  and  unde- 
viating  regularity  and  certainty  ;  they  have  also  the  remarkable 
property  of  being  so  amenable  to  the  laws  of  quantity  and  ma- 
thematics, as  to  be  in  most  instances  as  firmly  established  upon 
reason  as  abstract  truths  themselves.  The  mind  of  a  Newton 
was  chosen  to  reveal  these  laws  to  man,  and  man's  acquaintance 
with  them  may  be  justly  considered  as  one  of  his  noblest  privi- 
leges. To  point  out  their  wonders  in  detail,  and  the  sublime 
conclusions  to  which  they  lead,  is  the  business  of  a  colleague ; 
at  present  we  have  to  consider  them  in  their  more  general  form 
only,  and,  except  in  a  single  point  of  view,  as  objects  of  compa- 
rison merely  with  those  more  immediately  connected  with  our 
own  subject. 

The  point  of  view  to  which  we  allude  is  that  peculiar  case,  or 
instance  of  gravitating  force,  termed  iveight.  In  our  illustration 
of  the  attractive  forces  of  matter  above  given  w^e  supposed  a  case 
in  which  one  ball  was  very  much  larger  than  the  otlier:  now  this 
precisely  corresponds  with  the  case  of  the  globe  of  the  Earth,  and 
of  all  common  bodies  near  its  surface.  The  earth  is  more  than 
1,000,000,000,000,000  times  the  mass  of  any  body  which  is  ob- 
served to  fall  on  its  surface,  and  therefore  if  even  the  largest  body 
which  can  come  under  observation  M^ere  to  fall  tlirouijh  a  height 
of  500  feet,  the  corresponding  motion  of  the  Earth  would  be 
through  a  space  less  than  the  1,000,000,000,000,000th  part  of 
500  feet,  which  is  less  than  the  100,000,000,000th  part  of  an  inch, 
and  therefore  quite  inappreciable.*  Now  the  attractive  force  ex- 
erted between  the  earth  and  detached  bodies  is  denominated 
weight.  Hence  the  weight  of  a  body,  at  the  earth's  surface,  is 
proportionate  to  its  mass,  or  to  the  quantity  of  matter  it  may  con- 
tain, whatever  its  form  or  qualities  may  be — a  most  important 
fact  for  the  chemist,  who,  by  employing  the  chemical  properties 
of  bodies  as  indications  of  identity  or  of  change,  is  by  these  means 
enabled  to  apply  to  them  the  more  certain  measure  of  U'eight, 
and  thus  in  some  degree  to  bring  them  under  the  dominion  of  the 
laws  of  quantity. 

*  Lardner's  Cabinet  Cyclopaedia,  Art.  Mechanics,  p.  79. 


POLARIZING  FORCES.  35 

CHAPTER  III. 

OF  MOLECULAR  OR  POLARIZING  FORCES,  ETC. 

In  all  chemical  operations,  as  already  observed,  we  only  wit- 
ness the  beginning  and  the  end,  the  cause  and  the  effect,  while 
the  whole  of  the  intermediate  chancres  elude  our  senses.      Never- 
theless,  by  a  careful  observation  of  the  phenomena  we  are  enabled 
to  form  some  notion  upon  the  subject,  and  that  amply  sufficient 
to  convince  us  of  their  wonderful  nature.     With  a  view  therefore 
of  arresting  the  attention  of  those  who  may  be  unconscious  of 
these  wonders,  or  too  apt  to  overlook  them,  we  have  thought  it 
proper  to  premise  a  sketch  of  what  may  be  supposed  to   take 
place  among  the  ultimate  particles  of  which  all  bodies  are  consti- 
tuted, during  those  remarkable  changes  which  they  are  constantly 
undergoing.     And  here  it  may  be  remarked,  once  for  all,  that 
many  of  the  views  commonly  entertained  on  these  points  have 
always  appeared  to  us  to  be  so  imperfect  and  unsatisfactory,  that 
so  far  from  elucidating  the  subject,  they  have  only  served  to  ren- 
der it  the  more  obscure.     In  the  following  sketch,  therefore,  as 
better  adapted  for  our  purpose,  we  have  endeavoured  to  give  that 
view  of  the  subject,  which,  after  twenty  years  of  close  attention 
and  no  ordinary  labour,  we  have  been  induced  to  consider  as  the 
most  simple  and  consistent  with  the  phenomena.     The  general 
reader,  who  feels  no  interest  in  these  inquiries,  and  who  at  the 
same  time  wishes  to  be  apprized  of  the  nature  of  the  arguments 
deducible    from   the    divisibility   and   molecular   constitution    of 
matter,  is  referred  to  the  end  of  the  present  and  of  the  following 
chapters  for  a  summary  of  these  arguments. 

SECTION  I. 

Of  the  Divisibility  of  Matter, 

The  first  point  which  naturally  claims  our  attention  in  the 
consideration  of  molecular  operations,  is  the  size  of  these  mole- 
cules ;  a  subject  usually  discussed  under  the  head  of  the  divisi- 
bility of  matter.  Matter,  or  rather  space,  may  be  conceived  to 
be  divisible  ad  infinitum  ;  at  least  no  limits  can  be  assigned  be- 
yond which  its  subdivision  cannot  necessarily  proceed.  As  how- 
ever, it  exists  in  the  world  around  us,  there  cannot  be  the  least 
doubt  that  it  is  composed  of  ultimate  particles  or  molecules  inca- 


36  CHEMISTRY. 

pable  of  further  division  or  change,  at  least  by  ordinary  agents  : 
the  reasons  for  these  assertions  will  appear  hereafter,  at  present 
it  is  our  object  to  convey  to  the  general  reader  some  idea  of  the 
magnitude  of  these  particles,  with  the  view,  principally,  of  show- 
ing how  infinitely  they  surpass  the  limited  powers  not  only  of 
our  senses,  but  almost  of  our  conception.     The  subject,  however, 
has  so  much  attracted  the  attention  of  philosophers,  that  most  of 
our  readers  must  be  already  familiar  with  it ;  we  shall  therefore 
content  ourselves  with  merely  selecting  a  single  instance  from 
each  of  the  kingdoms  of  nature.     As  an  instance  from  the  mine- 
ral  kingdom,  we  may  quote  from  Dr.  Thomson,  who  has  shown 
that  an  ultimate  molecule  of  lead  cannot  weigh   more  than   the 
Troo"ooWoFo 0"  ^'^'    ^^^^  ^^   ultimate   molecule  of  sulphur  more 
than   foTJ'oo^o  0  0  0  0  0  ^^  ^^  ^  grain,  and  probably  a  great  deal  less; 
and  that  ihe  size  of  the  molecule  of  lead  cannot  surpass,  and  is 
probably  much  less   than  the   ^-s^-x-gro-gooooooo  ^^    of  a  cubic 
inch  !*     The  vegetable  kingdom   presents  us  with  innumerable 
instances,  not  only  of  the  extraordinary  divisibility  of  matter,  but 
of  its  activity,  in  the  almost  incredibly  rapid  developement  of  cel- 
lular structure  in  certain  plants.     Thus  the  Bovista  glgantcum 
(a  species  of  fungus),  has  been  known  to  acquire  the  size  of  a 
gourd  in   one  night.     Now  supposing,  with  Professor  Lindley, 
that  the  cellules  of  this  plant  are  not  less  than  the  -j-g-oth  of  an  inch 
in  diameter,  a  plant  of  the  above  size  will  contain  no  less  than 
47,000,000,000  cellules  ;   so  that,  supposing  it  to  have  grown  in 
the  course  of  twelve  hours,  its  cellules  must  have  been  developed 
at  the  rate   of  nearly  4,000,000,000  per   hour,  or  of  more  than 
sixty -six  millions  in  a  minute  !t  and  when  we  consider  that  every 
one  of  these  cellules  must  be  composed  of  innumerable  molecules, 
each  one  of  which  is  again  composed  of  others,  we  are  perfectly 
overwhelmed  with  the  minuteness  and  number  of  the  parts  em- 
ployed in  this  single  production  of  nature.     Rut  the  animal  king- 
dom perhaps  presents  us  with  still  more   striking  instances  than 
these.     Tiius   animalcules  have  been  discovered  whoso  magni- 
tude is  such  that  a  million  of  them  does  not  exceed  a   grain  of 
sand  ;  and  yet  each  of  these  creatures  is  composed  of  members  as 
curiously  organized  as  those  of  the  largest  species;  they  have  life 
and  spontaneous   motion,  and  are  endowed  with  feeling  and  in- 
stinct.    In  the  liquids  in  whicii   thev  live  thev  are  observed  to 
move  with  astonishing  speed  and  activity,  nor  are  their  motions 
blind  and   fortuitous,  but  evidently  governed  by  choice  and  di- 
rected to  an  end.     They  use  food  and  drink,  from  w^hich  they 

•  System  of  Inorg-anic  Chemistry,  I.  7. 
f  Introduction  to  Botany  page  7. 


DIVISIBILITY  OF  MATTER.  37 

derive  nutrition,  and  are  therefore  provided  with  a  digestive  ap- 
paratus. They  have  great  muscular  power,  and  are  provided 
with  limbs  and  muscles  of  strength  and  flexibility.  They  are 
susceptible  of  the  same  appetites  and  obnoxious  to  the  same  pas- 
sions. Must  we  not  conclude  that  these  creatures  have  hearts, 
arteries,  veins,  muscles,  sinews,  tendons,  nerves,  circulating 
fluids,  and  all  the '  concomitant  apparatus  of  a  living  organized 
body  ?  and  if  so,  how  inconceivably  minute  must  these  parts  be  ? 
If  a  globule  of  their  blood  bears  the  same  proportion  to  their 
whole  bulk,  as  a  globule  of  our  blood  bears  to  our  magnitude, 
what  power  of  calculation  can  give  an  adequate  notion  of  its  mi- 
nuteness ?* 

We  have  thus  endeavoured  to  convey  some  idea  of  the  mag- 
nitude of  the  ultimate  molecules  of  which  bodies  are  composed; 
but  though  we  have  succeeded  in  showing  that  they  cannot  ex- 
ceed a  certain  magnitude,  we  are  by  no  means  certain  that  they 
are  not  in  reality  much  lesS'— indeed  a  great  deal  less  than  the 
least  magnitude  of  which  we  have  endeavoured  above  to  convey 
a  conception:  yet  notwithstanding  this  inapproachable  minute- 
ness, they  retain  all  the  characters  of  matter  in  the  highest  de- 
gree, and  moreover  possess  certain  remarkable  properties  in  com- 
mon, upon  the  nature  of  which,  in  the  next  place,  we  have  to 
make  a  few  remarks. 

Section  II. 

Of  the  Forms  of  ^Aggregation  of  the  ultimate  Molecules  of 

Matter. 

Matter  in  the  aggregate,  and  as  it  appears  to  exist  in  the 
world  around  us,  is  known  to  us  principally  in  three  forms  or 
conditions  :— the  Solid,  the  Liquid,  and  the  Gaseous  (the  latter 
including  the  state  of  vapour  and  the  etheriform  condition  of 
matter)  ;  these  in  their  well  marked  states  are  sufficiently  distinct, 
though  the  whole  graduall}^  run  into  each  other ;  the  solid  into 
the  liquid,  and  the  liquid  into  the  gaseous,  by  such  imperceptible 
grades,  that  in  many  instances  it  is  not  easy  to  say  where  one 
ends  and  the  other  begins.t  The  notions,  which  the  mechanician 
or  natural  philosopher  employs  in  reasoning  on  these  forms 
of  bodies  are — of  a  solid,  that  all  its  parts  are  indissolubly  and 

*   Lardner's  Cyclopedia,  Art.  Mechanics,  p.  13. 

f  It  may  be  proper  here  to  observe  that  some  bodies,  as  water,  for  in- 
stance, are  capable  of  existing-  in  that  perfectly  g-aseous  form  denomi- 
nated vapour,  under  all  ordinary  circumstances  ;  thus  even  ice  gives  off 
vapour  rapidly,  as  we  shall  find  hereafter. 

4 


38  CHEMISTRY. 

unalterably  connected,  and  impenetrable,  so  that  the  relative  situ- 
ation of  the  parts  among  one  another,  cannot  be  changed,  or  one 
part  be  set  in  motion  without  all  the  rest ;  of  a  liquid,  that  all  its 
parts  are  freely  moveable  among  one  another,  but  that  it  is  not 
dilatable  or  compressible  by  mechanical  means  ;  of  a  gas  or  aeri- 
form body,  that  all  its  parts  are  not  only  freely  moveable  among 
one  another,  but  that  it  is  compressible  and  dilatable  without 
limits.  Strictly  speaking,  however,  there  are  no  objects  in  nature 
actually  existing  which  completely  conform  to  these  definitions : 
no  solid,  for  instance,  absolutely  hard  and  impenetrable,  no  fluid 
not  compressible  and  dilatable,  no  gas  compressible  or  dilatable 
without  limits :  and  these  circumstances  are  evidently  the  natural 
result  of  their  being  composed  of  aggregations  of  the  minute  mole- 
cules we  have  been  considering.  Thus  solids  composed  of  such 
molecules  must  necessarily  have  innumerable  interstices  or  pores  ; 
hence,  when  submitted  to  pressure,  they  are  liable  to  undergo 
more  or  less  of  condensation,  and  apparently  occupy  less  space 
than  before  :  the  same  remarks  may  be  made  with  respect  to 
liquids  ;  while  gaseous  bodies,  supposed  to  be  composed  of  such 
molecules,  of  course  cannot  be  intinilely  compressible. 


Section  III. 
Of  the  solid  Form  of  Bodies,     Crystallization, 

Natural  solids  present  us  with  a  variety  of  properties  usually 
termed  secondary^  many  of  which  are  of  the  utmost  importance  : 
such  are  hardness  and  softness,  elasticity,  toughness,  mallea- 
bility,  tenacity,  ductility,  &lc.,  all  too  well  understood  to  require 
definition  here.  These  properties  evidently  depend  in  a  great 
degree  upon  original  differences  in  the  properties  of  the  compo- 
nent molecules  themselves  ;  but  there  is  no  doubt  that  many  of 
them  are  also  intimately  connected  with  the  modes  in  which  the 
molecules  are  arranged.  Of  these  modes  we  can  form  no  pre- 
cise idea  in  a  great  many  instances  :  there  is,  however,  one  form 
of  solid  aggregation,  the  regidar  crystalline  form,  which  has 
occupied  much  more  attention  than  the  rest,  and  upon  this  we 
shall  proceed  to  offer  a  few  remarks. 

As  an  object  of  illustration  we  shall  select  the  familiar  one  of 
water,  which  from  its  well  known  properties  of  existing  either 
as  a  solid,  a  liquid,  a  vapour,  or  a  gas,  by  a  slight  variation  of 
circumstances,  is  well  adapted  for  our  purpose,  as  we  are  thus 
enabled  to  employ  the  same  object  of  illustration  throughout.  At 
present  we  have  to  consider  it  in  its  solid  form  of  ice. 


SOLID  FORM  OF  MATTER.  39 

Every  one  must  have  remarked  that  water  in  the  act  of  freez- 
ing assumes  various  symmetrical  forms,  shooting  into  speculae, 
&;c.,  as  may  be  beautifully  seen  on  our  windows  on  a  frosty 
morning.  Now  this  affords  a  familiar  instance  of  what  is  termed 
crystallization,  a  property  apparendy  possessed  by  all  pondera- 
ble matter,  and  readily  exhibited  by  it  when  under  favourable 
circumstances :  and  it  has  been  remarked  that  the  form  assumed 
by  the  same  matter  is  usually  similar,  or  easily  deducible  from 
some  common  form  according  to  well-ascertained  and  obvious 
laws.  Let  us  now  briefly  inquire  into  the  properties  which  the 
ultimate  molecules  of  water  must  be  supposed  to  possess  to  enable 
them  to  form  these  symmetrical  aggregations.  In  the  first  place 
it  is  evident  that  the  simple  supposition  of  mutually  attractive 
forces  between  these  molecules,  analogous  or  identical  with  the 
forces  of  gravitation,  is  inadequate  to  explain  the  phenomena. 
Possessed  of  such  properties  alone  the  ultimate  molecules  of 
bodies  might  indeed  be  imagined  to  adhere  together,  and  their 
aggregations  might  even  exhibit  something  like  regularity,  but 
this  regularity  would  in  a  great  measure  be  accidental,  and  proba- 
bly never  twice  alike  ;  hence  the  utmost  latitude  of  assumption 
would  never  enable  us  to  explain  upon  such  principles  alone  that 
sameness  of  figure  above  alluded  to  as  always  assumed  by 
the  same  matter.  It  is  obvious,  therefore,  that  the  ultimate 
molecules  of  bodies  are  influenced  by  other  powers  than  those  of 
simple  inertia  and  attraction  :  what  is  the  nature  of  these  powers  ? 
On  this  point  there  have  been  various  opinions.  Some  have 
supposed  the  ultimate  particles  of  bodies  to  possess  shapes  iden- 
tical with  those  of  the  aggregates  which  they  form  ;  that  a  crystal, 
for  example,  whose  shape  is  a  cube,  is  formed  by  the  aggregation  of 
a  number  of  infinitely  little  cubes,  &c.  But  to  others  this  supposition 
has  appeared  so  improbable,  and  so  unlike  the  usual  simplicity  of 
nature's  operations,  that  they  have  rejected  it,  and  have  formed  the 
more  feasible  hypothesis,  that  the  ultimate  molecules  of  bodies 
are  either  spheres,  or  spheroidal,  that  is  to  say,  more  or  less,  virtu- 
ally globular.*     Let  us  take  it  for  granted  then  that  the  ultimate 

•  Strictly  speaking",  perhaps  tliis  observation  is  applicable  to  the  forms 
supposed  to  be  assumed  by  the  influences  surrounding'  the  molecules, 
and  by  which  all  then'  operations  are  directed,  rather  than  to  the  abso- 
lute forms  of  the  molecules  themselves,  which,  thoug'h  in  all  instances 
virtually  exerting"  spheroidal  influences,  must,  in  different  instances, 
have  ve-ry  different  forms.  Those  who  wish  to  study  the  principles  upon 
which  spheroidal  molecules  may  be  supposed  to  ag"gregate  into  crystal- 
line forms,  are  referred  to  Dr.  WoUaston's  interesting"  paper  on  the  sub- 
ject in  the  Philos.  Trans.  1813,  p.  51.  It  may  be  noticed,  however,  that 
the  principles  here  advanced  differ  materially  in  other  respects  from  those 
referred  to. 


40 


CHEMISTRY. 


Fig.  1. 


i 


T7 


molecules  of  bodies  are  spheres,  with  what  powers  is  it  necessary 
to  suppose  these  little  spheres  to  be  invested  in  order  to  enable 
them  to  cohere  and  form  the  symmetrical  figures  we  observe 
among  natural  bodies?  The  existence  of  simple,  mutual  and  ge- 
neral attractive  powers  among  such  a  set  of  molecules,  has  been 
already  observed  to  be  inadequate  to  explain  the  phenomena  ; 
there  must  be  some  specific  powers  determining  similar  parti- 
cles, to  combine  in  similar  ways,  otherwise  the  same  resulting 

forms  could  not  be  supposed  to  take 
place.     In  the  tliree  small  spheres,* 
(Fig.   1.)  let  us  suppose  the  points 
Ec^  Ee,  Ee.  on  their  superficies  to 
be  endowed  with  the  following  pro- 
perties, viz.   that  the  similar  points, 
E,  E,  E,  and  c,  c,  e,  have  the  pro- 
perty of  mutually  repelling  each    other,  while  the 
dissimilar  Ee,  Ee,  Ee,  have  the  properly  of  mutual 
attraction.     In  such  a  case  the  three  molecules  will 
readily  combine  E  to  e,  as  in  Fig.  2,  but  in  no  other 

way.     Now    let    us 
suppose     the     same 
three   spheres  to  be 
endowed    with    pro- 
perties at  the  points 
31  m.    Mm,    Mm, 
as  in    Fig.   3,    very 
similar  to  those  at  E  e.     Spheres  so 
endowed  will  aggregate  readily,  as  in 
Fig.  4:,  E  io  e  and  M  \.o  m,  but  in  no 
other  way  ;  and  thus  instead  of  a  sin- 
gle  line  wc  obtain  a  plate  of  molecules 
one  in  thickness.t     To  form  th.e  third 
dimension,  or  to  constitute  a  solid,  it 
is  necessary  to  assume  the  molecules 
as  in  fig.  5,  to  be  possessed  not  only 
of  the  attractive  points  E  e,  E  e,  E  e, 


( 


*  Or  rather  sections  of  .spiieres,  .and  the  same  is  to  be  understood  of 
all  the  subsequent  figures. 

t  Here  it  is  to  be  observed  tliat  tlie  similar  poles  E  E,  e  e,  of  each 
pair  of  molecules  being-  supposed  lo  be  repellent  within  certain  limits,  as 
will  hereafter  be  explained,  their  absolute  contact  is  prevented,  and  the 
two  molecules  are  l)alanccd,  as  it  were,  between  the  two  opposing-  and  the 
two  attracting  forces,  'I^he  consideration  of  forces  operating  in  these  and 
in  the  otlicr  modes,  suhsequcntl}'  mentioned,  present  some  highly  in- 
teresting and  novel  objects  of  researcli  for  the  mathematician. 


CRYSTALLIZATION. 


41 


L^X2^^ 


3Imy  Mm,  Mm,  but  also  of 
M'  m\  M'  m'y  M'  m',  (the 
point  m',  being  supposed  to  be 
opposite  to  the  point  M',  and 
out  of  sight.)  Molecules  so 
endowed  will  readily  combine 
as  in  Fig.  6,  and  form  a  cube 
or  some  figure  obviously  dedu- 
cible  from  it,  but  in  no  other 
manner ;  and  in  this  way  by 
assuming  certain  attractive  and 
repulsive  points  upon  our 
spheres  at  appropriate  parts  of 
their  superficies,  it  is  not  difl[i- 
cult  to  conceive  them  capable, 
in  different  instances,  of  form- 
ing aggregates  of  any  shape  whatever.  The  next  point  to  be 
considered  is,  how  far  are  we  authorized  in  making  such  appa- 
rently complicated  and  gratuitous  assumptions  respecting  the  pro- 
perties of  the  ultimate  molecules  of  matter;  are  there  any  pheno- 
mena in  nature  justifying  such  conclusions,  and  what  are  they  ? 
And  this  leads  us  to  inquire  further,  but  as  briefly  as  possible, 
into  the  phenomena  of  aggregation,  as  we  see  them  constantly 
going  on  around  us. 

Aggregation  is  usually  considered  as  of  two  distinct  kinds,  viz. 
that  depending  upon  the  simple  cohesion  of  similar  molecules  of 
matter,  as  of  water,  and  which  for  the  present  may  be  svipposed 
to  undergo  no  change  by  the  combination  ;  and  that  depending 
upon  the  union  of  dissimilar  molecules  of  matter,  capable  of  ex- 
erting a  mutual  chemical  change  upon  each  other,  in  which  case 
the  aggregate  is  a  teriium  quid,  or  third  something  differing  alto- 
gether from  either  of  the  original  molecules  composing  it.  Now  both 
these  kinds  of  aggregation  obviously  exist  in  the  same  substance, 
at  least  when  in  the  solid  form.  In  the  first  place  the  chemical 
aggregation  is  exerted  between  the  heterogeneous  molecules, 
(hydrogen  and  oxygen  in  the  present  case  of  water)  which  uniting, 
form  compound  homogeneous  molecules,  (of  water) ;  while  in  the 
next  place,  the  molecules  of  water  uniting  chemiccdly  in  one  di- 
rection and  cohesively  in  the  other,  form  the  solid  crystal  (of 
ice).  Hence  chemical  aggregation  and  cohesive  aggregation  are 
as  distinct  as  the  polarities  themselves  upon  which  they  depend ; 
and  if  the  one  existed  alone  without  the  other,  no  such  thing  as  a 
regular  crystalline  solid  would  probably  be  formed  in  nature. 
From  the  above  views,  of  molecular  forces,  it  follows  as  a 

consequence  that  every  molecule,  and  crystalline  aggregate    of 

4« 


42  CHEMISTRY. 

molecules,  must  possess  one  axis  (as  lliat,  for  instance,  joining  the 
polarities  E  e  in  tlie  preceding  figures,)  having  totally  different 
powers  and  properties  from  the  other  two  axes  and  polarities. 
This  axis,  by  way  of  distinction,  may  be  called  the  chemical  axis 
and  polarities.  The  other  two  axes  (and  indeed  every  other  axis 
that  can  be  supposed  to  be  drawn,  through  the  centre,  from  oppo- 
site points  of  the  superficies  of  the  molecule)  probably  possess 
common  properties,  and  may  be  called  the  cohesive  axes  and  po- 
larities. Here  then  the  existence  of  two  forces  is  indicated, — the 
one  axial,  the  other  equatorial,  if  we  may  be  allowed  the  expres- 
sions. The  next  question  is,  do  such  forces  actvially  exist  in  na- 
ture on  the  large  scale,  and  what  are  these  forces  ?  Now  late  ob- 
servations have  proved,  beyond  a  doubt,  that  the  electric  and 
magnetic  are  such  forces.  We  proceed,  therefore,  to  take  a  short 
view  of  electricity  and  magnetism.* 

Electricity. — It  would  be  foreign  to  our  present  purpose  to 
enter  into  details  respecting  this  or  any  other  department  of 
science  we  may  have  occasion  to  allude  to  :  hence  we  shall  con- 
tent ourselves  with  a  short  summary  of  its  general  principles.  It 
seems  to  be  satisfactorily  proved  that  the  phenomena  of  electrici- 
ty depend  upon  two  energies,  usually  existing  throughout  nature 
in  a  state  of  equilibrium,  in  which  slate  their  peculiar  powers  are 
not  perceptible  ;  that  this  equilibrium  is  capable  of  being  destroy- 
ed by  a  variety  of  causes,  as  friction,  &c. ;  and  that  owing  to  the 
different  capacities  possessed  by  different  bodies,  for  conducting 
and  retaining  them,  these  energies  can  be  partially  separated  and 
kept  asunder,  in  which  state  they  are  capable  of  exhibiting  their 
peculiar  powers.  These  powers  are  such,  that  if  two  bodies 
charged  in  excess  with  the  same  energy  be  brought  into  the  vicini- 
ty of  each  other,  they  mutually  repel  each  other ;  while  two 
bodies  charged  with  the  two  different  energies  mutually  attract 
each  other.  In  this  disturbance  of  the  equilibrium  of  the  two 
energies,  it  is  to  be  remarked,  that  in  no  instance  do  we  suppose 
that  the  two  energies  are,  or  ran  be,  entirely  separated,  so  as  to 
reside  each,y;er  se,  in  different  bodies  ;  but  that  a  portion  of  the 
energy  of  the  one  body  goes  to  the  other  body,  which  at  the  same 

*  It  may  be  rcmnrkcd,  tliat  as  all  parts  of  the  superficies  of  our  mole- 
cules, except  the  cJiemicul  poles,  are  supposed  to  be  more  or  less  capable 
of  cohesion,  their  ag'g-ret^'ation  in  the  form  of  common  crystallized  solids 
may  be  readily  conceived.  With  respect  to  the  cohesion  (if  we  may  be 
allowed  the  expression)  of  the  diflerent  chemical  poles  E  c,  of  similar 
molecules  with  each  otlier,  such  coliesion  seems  to  be  proved  by  several 
circumstances,  which  it  would  be  foreign  to  our  purpose  at  present  to 
inquire  into  ;  hut  of  wliicli,  perhaps,  the  optical  ];)i-o])erties  of  crj'stuls 
will  hereafter  form  one  of  the  most  striking  illustrations. 


ELECTRICITY.  43 

time  returns  a  corresponding  portion  of  its  antagonist  energy; 
hence,  other  tilings  being  equal,  eacli  body  contains  the  same  total 
quantity  of  the  two  electricities  as  before  the  equilibrium  was  de- 
stroyed. For  the  sake  of  the  general  reader,  the  matter,  in  short, 
may  be  represented  numerically  as  follows  : — Let  us  suppose 
that  2000  balls,  all  exactly  of  the  same  size,  Slc,  but  one  half 
black  and  the  other  half  white,  are  divided  into  two  equal  groups, 
A  and  B,  of  1000  balls  each,  but  in  such  a  way  that  the  group  a 
shall  contain  200  black  and  800  white  balls,  and  the  group  b  800 
black  and  200  white  balls.  In  this  case  th.e  two  groups  will  cor- 
respond exacdy  with  two  bodies  in  different  states  of  electricity  ; 
and  (supposing  them  to  be  possessed  of  similar  powers),  if  a  third 
group,  c,  containing  200  black  and  800  white  balls  be  brought  into 
the  neighbourhood  of  the  group  a,  which  is  similarly  constituted, 
the  two  will  be  found  mutually  to  repel  each  other,  till  they  ap- 
proach within  a  certain  distance,  that  is  to  say,  till  the  200  ijlack 
balls  of  each  group  come  into  action,  and  unite  each  with  200 
white  balls.  At  this  distance  they  will  no  longer  repel  but  attract 
each  other;  although,  instead  of  forming  a  state  of  equilibrium, 
the  white  balls  (or  one  of  the  electric  energies,)  will  predominate. 
The  same  thing  precisely  may  be  supposed  to  happen  if  a  fourth 
group,  D,  composed  of  800  black  and  200  white  balls,  be  brought 
into  the  neighbourhood  of  the  group  b.  But  if  the  group  a,  con- 
taining 200  black  and  800  white  be  brought  into  the  neighbour- 
hood of  tlie  group  b,  containing  800  black  and  200  white,  the  two 
will  attract  each  other,  and  combine  to  form  the  original  group  of 
2000  balls,  consisting  of  1000  of  each  kind,  as  at  first  supposed. 

Such  are,  we  believe,  the  fundamental  laws  of  action  and  equi- 
librium of  the  two  electric  energies.  There  is  one  circumstance 
immediately  arising  out  of  them,  which,  as  it  is  the  most  frequent 
and  important  of  all  the  causes  disturbing  the  natural  equilibrium 
of  the  two  energies  in  diflerent  bodies,  we  shall  briefly  explain  : 
we  allude  to  what  are  usually  called  the  phenomena  oi  inductio7i. 
Suppose  an  electrified  body  a,  (that  is  to  say,  a  body  having  the 
equilibrium  of  its  electric  energies  destroyed,  as  above  mention- 
ed,) be  brought  into  the  neighbourhood  of  another  body,  b,  in  its 
natural  state,  what  takes  place  ?  The  electricity  e,  of  the  body 
A,  acting  upon  the  corresponding  electricity  e,  in  the  body  b, 
repels  it  to  the  furthest  extremity  of  the  body  b  ;  and  at  the  same 
time  attracts  to  that  end  of  the  body  b  whicli  is  nearest  to  the 
body  A,  the  other  and  opposite  electricity  e.  The  body  b,  there- 
fore, while  under  the  influence  of  the  body  a,  will  exhibit  all  the 
phenomena  of  electricity,  and  is  said  to  be  electrified  by  induc- 
tion ;  but  remove  this  body  b  from  the  neighbourhood  of  the 
body  a,  and  immediately  the  natural  equilibrium  of  the  energies 


44  CHEMISTRY. 

of  the  body  b  will  be  restored,  and  all  signs  of  electricity  will 
vanish.  In  this  experiment  neither  of  the  bodies  gains  or  loses 
anything.  As  these  phenomena  are  constantly  occurring  in  nature, 
and  as  we  shall  have  frequent  occasion  to  use  the  term  induction^ 
we  have  endeavoured  to  convey  an  idea  of  the  nature  of  the  sub- 
ject to  the  general  reader. 

Of  Galvanism. — >While  we  are  upon  the  subject  of  electricity, 
we  may  briefly  notice  that  important  modification  of  it  termed 
galvanism.  This  form  of  electricity,  instead  of  being  evolved  by 
friction,  is  usually  obtained  by  the  mutual  action  of  various  metals 
and  chemical  agents  upon  each  other.  Late  experiments,  how- 
ever, have  shown  that  the  energies  thus  developed,  differ  in  no 
respect  from  those  of  common  electricity,  but  that  they  are  ob- 
tained in  this  way  in  much  greater  quantity  only,  though  in  a 
lower  state  of  intensity  than  by  the  common  machine  ;  and  that 
many  of  the  supposed  peculiar  eflects  of  galvanism  are  the  con- 
sequence of  the  motion  of  such  large  quantities  of  these  energies, 
through  bodies  of  various  conducting  powers.  Galvanism  has 
recently  attracted  much  more  attention  than  ordinary  electricity, 
from  the  facility  with  which  it  may  be  applied  to  the  purposes  of 
the  chemist,  and  from  the  extraordinary  light  it  has  thrown  upon 
many  chemical  phenomena.  Indeed,  the  chemist  has  been  more 
indebted  to  the  energies  of  galvanism  than  to  any  other;  and  he 
will  probably  be  still  further  indebted  to  them  than  he  yet  has 
been.  With  respect  to  the  phenomena  of  galvanism,  these  in 
most  respects,  so  closely  resemble  the  phenomena  of  electricity, 
that  they  do  not  require  further  illustration  here. 

Of  Magnetism. — The  general  phenomena  and  laws  of  magnet- 
ism are  very  analogous  to  those  of  electricity.  There  are  evi- 
dently two  antagonist  energies,  which,  while  in  a  stale  of  equi- 
librium, are  not  cognizable  ;  but  when  separated,  each  one  is 
mutually  repellant  of  its  similar,  and  mutually  attractive  of  its  op- 
posite or  antagonist.  Thus  the  two  north  or  two  south  poles  of 
two  magnetic  needles  mutually  repel  each  other  (with  the  same 
exceptions  as  the  two  electric  poles),  but  the  north  pole  of  one 
needle  and  the  south  pole  of  another,  mutually  attract  each  other. 
Bodies  are  also  rendered  magnetic  by  induction  when  in  the  vici- 
nity of  another  magnet,  precisely  as  happens  with  respect  to  elec- 
tricity. Magnetism  principally  differs  from  electricity  in  being 
apparently  limited  to  a  few  bodies,  as  iron,  and  two  or  three  others ; 
but  late  observations  have  thrown  an  entirely  new  light  on  this 
part  of  the  subject,  which  we  have  next  to  consider.  Before  we 
proceed,  however,  we  may  make  a  few  remarks  upon  the  obvi- 
ous questions  : — What  becomes  of  the  two  electric  and  two  mag- 
netic energies  when  in  a  state  of  equilibrium  ?  Do  the  electric  and 


/:i  c 


M< — 


-m 


ELECTRICITY  AND  MAGNETISM.  45 

magnetic  energies  combine  to  yield  the  same,  or  a  diflerent  re- 
sult, and  what  is  the  nature  of  this  result  or  results,  and  in  what 
form  do  they  exist  around  us?  On  these  points  difrtrcnt  opinions 
have  been  lield  :  some  supposing  that  by  their  union,  both  tlie  elec- 
tric and  the  mngnetic  energies  alike  constitute  heat ;  others  some- 
thing else.  That  both  are  most  intimately  connected  with  heat 
and  light,  is  evidewt ;  but  at  present  we  decline  to  give  a  decided 
opinion  on  the  subject. 

We  come  now  to  consider  the  relations  of  electricity  and  of 
magnetism  to  one  another — a  discovery  which  we  owe  to  Oer- 
sted, and  one  of  the  most  important  that  has  been  made  in  the  pre- 
sent age.     The  following  is  a  summary  of  these  relations.     Let 
Fig-.  7.  lis  suppose,  in  the  annexed  figure,  E  e,  to  repre- 

sent the  wire  connecting  the  zinc  and  the  cop- 
per terminating  plates  of  a  galvanic  battery  in 
action.  From  what  has  been  said,  it  may  be 
conceived  that  under  these  circumstances  there 
will  be  two  currents  moving  through  this  wire 
in  opposite  directions ;   (from  the  copper  to  the 

_._ zinc,  usually  called   positive  electricity,   which 

oappi^r  I  p-jj^y  j^g  supposed  to  be  represented  by  our  black 

balls  in  the  previous  illustration  ;  and  from  the  zinc  to  the  cop- 
per, usually  termed  negative  electricity,  which  may  be  represented 
by  our  white  bails).  Now  in  this  state  of  things  it  has  been  sa- 
tisfactorily established  by  experiment,  that  besides  these  two  cur- 
rents, there  are  two  others  having  totally  different  properties, 
indeed  all  the  properties  of  the  magnetic  energies,  moving,  not  in 
the  direction  of  the  wire,  but  in  circles,  or  rather  spirals, 
round  it.  The  energy  corresponding  to  the  north  pole  of  the 
magnetic  needle  moves  from  right  to  left,  round  the  wire,  as 
above  posited,  while  the  energy  corresponding  to  the  south  pole 
of  the  magnet  moves  in  the  opposite  direction,  or  from  left  to 
right.  Hence  when  a  delicate  magnetic  needle  M "tn,  is  placed 
above  the  wire  E  e,  its  north  pole  M,  will  be  attracted  by  the 
current  moving  from  left  to  right,  with  which  it  comes  first  in 
contact ;  and  its  south  pole,  for  similar  reasons,  will  be  attracted 
by  the  opposite  current.  A  needle  so  placed  will  consequently 
assume  the  direction  represented  in  the  figure,  with  its  north 
pole  M  to  the  left  ;  and  if  it  be  carried  round  the  wire  by  its 
point  of  suspension,  it  will  be  always  found  to  keep  the  same 
relative  position  with  respect  to  the  wire.  Thus  when  below  the 
wire,  the  needle  will  apparently  point  in  the  opposite  direction  ; 
when  on  the  same  level,  on  the  left  hand,  vertically  downwards; 
w^hen  on  the  right,  upwards. 

Bearing  in  mind  these  relative  positions  of  the  currents  and 


46 


CHEMISTRY. 


needles,  in  what  follows  we  may  neglect  the  currents  and  judge 
from  the  posiiion  of  the  needles  alone.  Let  us  consider  the  case 
of  two  connecting  wires  placed  by  the  side  of  each  other,  as  in 
the  figures  annexed,  and  which  wires  may  be  supposed  to  repre- 


M< — 


c 

j    Copp&r 


Fig.  8. 


I     Zf'iic     I 


Zffic    \ 


-TTl    3K- 


E 


-VI 


Cupper  I 


Fig-.  9. 


Ziric 

\E 


M- 


u^ 


-VI 


VI- 


Coppci^ 


Copper 


E 


Zinc    i 


sent  the  chemical  axis  of  our  molecules.  Now  these  wires,  in 
consequence  of  the  magnetic  energies  circulating  round  them, 
will  mutually  attract  or  repel  each  other,  according  to  tiieir  posi- 
tion. If  as  in  fig.  8,  they  are  both  in  the  same  relative  position, 
they  will  mutudly  attract  each  other,  as  may  be  inferred  from  the 
position  of  the  needles,  Mrn^  Mm,  the  north  pole  of  one  of 
which  corresponds  wiih  the  south  pole  of  the  other ;  but  if  one 
of  the  wires  be  reversed,  as  in  fig.  9,  they  will  mutually  repel 
each  other,  the  two  similar  poles  of  the  needles  in  this  case 
being  contiguous.  These  relations  hold  universally,  and  what  is 
most  important,  recent  observations  have  shown  them  to  be  re- 
ciprocal ;  that  is  to  say,  if  the  magnetic  energies  be  made  to 
move  in  straight  lines,  the  galvanic  energies  are  found  to  circu- 
late round  them  precisely  in  the  way,  and  according  to  the  laws 
above  described  as  happening  to  magnetism  round  electricity. 
Hence  electric  sparks,  and  indeed  all  the  phenomena  of  electri- 
city can  now  be  obtained  from  a  common  maornet. 

Whether  electricity  and  magnetism  be  different  forms  of  the 
snme  energies  resulting  from  the  difierent  directions  of  their  mo- 
tions— whether  they  be  distinct  energies — whether  they  be  the 
cause  or  tlie  effect  of  Polarity,  we  shall  not  stay  to  inquire  ;  it  is 
sufficient  for  our  present  purpose  to  know  that  they  are  insepara- 
bly associated  with  one  another  in  the  manner  stated,  and  are  al- 
ways present  at  least  in,  if  they  be  not  the  immediate  cause  of, 
all  molecular  actions  among  ponderable  bodies.  And  this  brings 
us  back  to  the  point,  where  we  digressed  to  consider  the  subjects 
of  electricity  and  magnetism. 

We  attempted  to  show  that  the  ultimate  molecules  of  matter 
must  possess  two  kinds  of  Polarity  ;  one  which  we  have  deno- 
minated Chemical  Polarity,  of  a  binary  character,  and  existing 


POLARIZATION,  ELECTRICITY,  ETC.  47 

between  molecule  and  molecule,  cliiefly  when  of  different  kinds ; 
and  another  denominated  cohesive  polarity,  determining,  under 
certain  circumstances,  molecules  of  the  same  matter  to  cohere. 
We  further  attempted  to  explain  how  these  polarities  (each  sup- 
posed to  be  connected  by  its  own  proper  axis)  must  exist  or  be 
distributed  in  our  molecules  so  as  to  fulfil  the  offices  assigned  to 
them,  and  which  they  evidently  fultil  in  nature.  Lastly,  we  have 
shown  that  the  electric  and  magnetic  polarities  or  energies  are 
actually  related  to  one  another,  precisely  in  the  same  way  that 
we  supposed  the  chemical  and  cohesive  polarities  to  be.  The 
question  then  at  once  arises, — are  these  forces  identical  ?  Do  the 
electric  polarities  correspond  with  the  supposed  chemical  polari- 
ties, and  the  magnetic  with  the  cohesive  polarities  of  our  mole- 
cule ? 

To  us,  we  have  no  hesitation  in  saying,  this  conclusion  seems 
very  probable,  nay,  almost  inevitable,  not  only  for  the  reasons 
stated,  but  for  others  equally  striking,  that  we  shall  have  occasion 
to  refer  to  hereafter.     In  the  mean  time  we  may  briefly  consider 
the  subject  with  a  little  more  attention,  and  principally  with  refer- 
ence to  some  apparent  objections  that  may  be  raised  against  it. 
In  the  first  place  it  may  be  objected  that  it  is  difficult,  from  what 
we  know  of  the  varying  and  capricious  character  of  the  electric 
energies,  to  suppose  that  they  can  ever  exist  in  that  definite  and 
permanent  form  in  which  they  must  exist  if  they  be  really  iden- 
tical with  the  cause  of  chemical  affinity.     To   this  objection,  it 
may  be  replied,  that  magnetism  can  and  does  exist  permanently 
in  bodies  for  ages,  and  as  electricity  is  an  inseparable   attendant 
upon  magnetism,  this   energy  must  also  have  equal  permanence. 
Again,  a  portion  of  zinc  and  a  portion  of  copper  placed  in  con- 
tact produce  electrical  effects  as  constant  and  enduring  as  the  me- 
tals themselves.       The  argument,   therefore,   founded  upon  the 
want  of  permanence,  and  uniformity  of  the  electric  and  magnetic 
energies,  cannot,  if  duly  considered,  be  supposed   to  have  any 
weight;  for  the  molecule  may  be  conceived  to  be  composed  of 
two  parts  analogous  to  the  copper  and  zinc  in  contact,  and  the  elec- 
tricity and  accompanying  magnetism   evolved  may  be  supposed 
to  be  as   permanent  in  their  character  as  the  parts  of  the  mole- 
cule evolving  them.     To  the  argument  that  electricity  and  mag- 
netism, as  we  are  acquainted  with  these  energies,  are  inadequate 
to  produce  the  effects  and  explain  the  phenomena  of  chemical 
affinity  and  cohesion,  it  may  be  replied,  that  they  may  be  so  : 
but  that  these  energies,  as  we  are  acquainted  with  them,  are  pro- 
bably merely  accidental  and  peculiar  modifications  of  the  real  en- 
ergies, which  in  their  elementary  form,  may  be   something  alto- 
gether difierent,  and  quite  unknown  to  us.     In  proof  of  this  no- 


48  CHEMISTRY. 

tion,  it  may  be  observed,  that  the  electricities  of  the  common 
machina  and  of  the  galvanic  machine  apparendy  differ  material- 
ly;  while  that  existing  in  certain  animals  appears  to  differ  from 
both.  The  magnetism  evolved  by  electricity  differs  also  slighUy 
from  common  magnetism,  yet  no  one  now  doubts  that  these  dif- 
ferences arise  from  varieties  in  the  quantity  and  intensity  of  the 
same  energies,  whicli  in  their  elementary  form,  therefore,  may, 
and  probably  do,  differ  from  all  these  varieties.  At  any  rate,  we 
are  unable  to  say  that  one  of  these  varieties  is  more  elementary 
than  another,  and  consequently  we  have  no  right  to  assume  that 
either  of  them  is  elementary,  much  less  to  found  any  argument 
upon  the  assumption. 

Before  we  quit  this  subject  of  polarities  and  polarizing  forces, 
it  may  not  be  amiss,  in  the  last  place,  to  make  a  few  general  re- 
marks on  tlie  points  in  which  they  resemble  or  difi'er  from  those 
of  gravitation. 

The  forces  of  gravitation,  inertia  and  attraction,  appear  to  be 
associated,  and  to  reside  in  every  individual  atom  of  matter  in  the 
universe  ;  hence  every  atom  mutually  attracts  and  is  attracted  by 
every  other  atom.  The  polarizing  forces,  on  the  other  hand,  are 
evidently  disassociated,  and  reside  in  different  parts  of  the  same 
mass  ;  hence  this  mass  can  in  no  instance  be  a  mathematical  point, 
(or  atom  ?),  but  must  consist  of  at  least  two  parts  ;  hence,  also,  as 
all  matter  appears  to  possess  polarity,  matter  must  exist  in  the 
state  of  mass  or  molecule^  each  of  which  molecules  must  occupy 
actual  space.  Thus  the  forces  of  gravitation  and  those  of  polari- 
zation are  quite  distinct.  The  forces  of  gravitation  are  primordial, 
and  probably  co-existent  with  matter  ;  while  the  forces  of  polari- 
zation have  more  of  a  derivative  or  resultant  cliaracter,  and  are 
evidendy  subordinate  to  those  of  gravitation.  The  question  here 
naturally  arises, — Are  these  difl^erent  forces  related  to  one  another  ? 
Do  the  forces  of  polarization  consist  of  the  forces  of  gravitation 
in  a  state  of  separation,  (if  we  may  be  allowed  the  expression,)  or 
do  they  result  from  the  motion  of  the  molecules  upon  their  axes? 
These  are  questions  quite  beyond  our  powders, — indeed  we  have 
nothing  to  do  with  them, — our  present  objectbeing  merely  to  point 
out  the  apparent  limits  within  which  the  Deity  has  chosen  to  con- 
fine his  operations. 

Section  IV. 

Of  the  Liquid  Form  of  Bodies.     Of  Heat. 

Hitherto  we  liave  spoken  of  tlie  a^-orregation  of  molecules  in 
the  solid  form  only  ;  we  have  next  to  consider  their  arrangement 


OF  HEAT.  49 

in  that  state  in  which  they  constitute  a  liquid.  Our  notion  of  a 
fluid,  generally  speakino^,  is,  tiiat  all  its  parts  or  molecules,  instead 
of  being  fixed,  are  perfectly  moveable  among  one  another ;  our 
notion  of  a  liquid  (the  least  perfect  form  of  fluidity)  is,  that  its 
molecules  are  incompressible.  Now,  still  retaining  water  as  our 
example  of  a  liquid,  let  us  consider  what  must  happen  to  its  mole- 
cules situated,  as  we  suppose  them  to  be,  in  the  form  of  ice,  be- 
fore they  can  be  so  arranged  as  to  constitute  the  liquid  water.  A 
moment's  reflection  teaches  us  that  they  must  be  loosened  or  se- 
parated from  each  other;  and,  as  they  cannot  separate  themselves, 
that  some  new  agency  is  requisite  for  this  purpose.  It  need  scarcely 
be  mentioned  that  this  agent  is  heat ;  on  the  general  phenomena 
and  laws  of  which  most  important  principle  we  now  proceed  to 
make  a  few  remarks. 

The  sensations  termed  hcaf.mvl  cold  are  too  well  known  to  re- 
quire explanation.  These  sensations,  however,  like  all  others, 
are  merely  the  effects  of  some  external  cause  or  causes,  operating 
on  and  through  our  organs,  in  a  manner  totally  unknown  to  us. 
Various  opinions  have  been  entertained  on  the  subject;  some  con- 
sidering the  cause  of  heat  (caloric)  to  be  an  existent  and  material 
fluid,  though  of  such  extreme  tenuity  and  imponderability  as  to 
escape  our  observation,  and  to  become  manifest  to  us  only  by  its 
effects  upon  our  sensations,  and  upon  all  ttie  ponderable  forms  of 
matter  ;  others  considering  it  not  as  material,  but  as  a  property  or 
principle  of  motion,  which  by  exciting  a  certain  species  of  vibra- 
tion among  the  particles  of  bodies  causes  the  sensations  and  effects 
of  heat.  Such  are  the  most  usual  opinions,  and  the  probability 
is,  that  they  are  neither  of  them  literally  correct,  but  that  heat,  and 
we  may  add  light,  are  substances,  the  molecules  of  which  are  in- 
fluenced by  polarizing  forces  precisely  similar  in  all  respects  to 
those  which  influence  common  matter  ;  that  is  to  say,  that  the 
molecules  of  heat  and  of  light  obey  laws,  similar  in  all  respects  to 
those  which  govern  the  molecules  of  ponderable  bodies.*  We 
have  already  alluded  to  the  opinion  maintained  by  some,  that  heat 
is  a  compound  principle  (like  water  for  instance),  consisting  of  a 
union  of  the  two  forms  of  electricity.  We  now  draw  the  attention 
of  the  reader  to  this  hypothesis,  in  order  to  state,  that  whatever 
heat  may  consist  of  besides,  it  is  almost  impossible  to  explain  its 

*  We  are  aware  trial  this  opinion  is  opposed  to  that  of  most  mathema- 
ticians, who  favour  the  undulatory  theory  of  light,  and  with  good  reason, 
so  far  as  they  have  occasion  to  consider  it ;  but  we  are  decidedly  of  opi- 
nion that  the  chemical  action  of  lig'lit  can  be  explained  only  upon  chemical 
principles,  whatever  these  may  be.  Whether  these  chemical  principles 
will  hereafter  explain  what  is  now  st  happily  illustrated  by  undulse,  time 
must  determine. 

5 


50 


CHEMISTRY. 


effects  upon  the  polarizing  forces,  without  supposing  that  it  at 
least  involves,  if  it  do  not  pass  into  the  electric  forces,  upon  which 
the  polarizing  forces  apj^ear  to  us  to  depend.  We  have  said  ap- 
pear,  for  as  has  been  already  stated,  though  it  is  convenient  to 
consider  the  polarizing  forces  under  the  forms  of  electricity  and 
magnetism,  in  which  they  are  most  usually  and  palpably  mani- 
fested to  us  among  ponderable  bodies,  yet,  in  their  elementary 
form  these  forces  may  in  reality  be  something  very  different,  not 
only  from  those  of  electricity  and  magnetism,  but  from  all  others 
with  which  we  are  acquainted  ;  while  electricity  and  magnetism, 
themselves,  may  be  nothing  more  than  the  effects  of  these  element- 
ary forces  upon  the  subtle  matters  of  which  the  electric  and  mag- 
netic molecules  are  composed. 

One  of  the  most  general  effects  of  heat  is  the  increase  of  volume 
which  it  produces  in  all  bodies  in  which  it  is  accumulated.  There 
are  a  few  exceptions  to  this  law,  and  one  of  so  curious  and  im- 
portant a  character  as  to  require  especial  notice  hereafter.  In  the 
mean  time,  however,  the  generality  of  the  law  may  be  taken  for 
granted,  and  an  attentive  comparison  of  what  has  preceded  and 
follows,  will  perhaps  throw  some  light  upon  the  nature  of  this 
phenomenon. 

Let  us  suppose  Fig.  10,  to  represent, 
as  in  our  former  illustrations,  two  mole- 
cules of  ice,  with  the  chemical  axes  E  e,  E  e, 
parallel  and  similar.  In  this  state  their  co- 
hesive polarities  will  be  dissimilar,  and  the 
molecules,  of  course,  will  cohere  as  repre- 
sented. Let  us  now  suppose,  from  some  external  source,  a  cer- 
tain quantity  of  heat  to  be  communicated  to  these  molecules.  The 
natural  tendency  of  heat  is  usually  considered  to  be  to  arrange 

itself  in  the  form  of  an  atmosphere,  around 
the  molecules  as  in  Fig.  11 ;  the  consequence 
of  which  is,  that  their  apparent  temperature 
is  raised  a  certain  quantity,  and  they  will 
be  separated  from  each  other  in  some  slight 
degree  ;  they  will  thus  occupy  more  space 
than  in  Fig.  10,  before  the  addition  of  heat;  the  cohesion  between 
the  parts  Mm  will  also  at  the  same  time  be  diminished.  And 
here  it  may  be  proper  to  notice  an  important  fact,  that  the  same 
quantity  of  heat  when  introduced  into  different  bodies  produces 
very  difierent  apparent  temperatures  and  effects,  and  that  this  con- 
stitutes what  is  called  by  chemists  their  capacity  for  heat,  or  their 
specific  heat.  Thus  if  the  same  quantity  of  heat,  which  we  sup- 
posed to  have  been  introduced  into  two  molecules  of  ice,  had  been 
introduced  into  two  molecules  of  silver,  their  apparent  temperature 
would  have  been  raised  more  than  ten  times  as  much  as  that  of 


CAPACITY  FO?^  HEAT,  ETC.  51 

the  molecules  of  ice  ;  hence  in  the  case  of  the  ice  some  of  the  heat 
must  have  disappeared,  or  become,  in  the  language  of  chemists, 
latent^  a  most  important  property  of  heat  which  we  have  next 
briefly  to  inquire  into.  Previously,  however,  it  may  not  be  amiss 
to  observe,  that  the  molecules  of  heat  are  supposed  to  be  vastly 
less  than  those  of  any  ponderable  substance  ;  and  that  they  may 
thus,  without  any  incongruity,  be  supposed  capable  of  forming  an 
atmosphere  around  the  ponderable  molecules,  which  they  could 
not  otherwise  of  course  be  imagined  to  do. 

The  latency  of  heat  appears  to  depend  upon  two  totally  differ- 
ent phenomena,  or  rather,  properly  speaking,  is  of  two  distinct 
kinds,  as  may  be  thus  illustrated.  Let  us  take  the  two  bodies 
above  alluded  to — ice  and  silver  ;  these  under  the  same  volume 
contain  very  unequal  portions  of  matter,  the  silver  being  ten  times 
as  heavy  as  the  ice.  The  vacuities  in  the  ice,  therefore,  must  be 
very  much  greater  than  those  in  the  silver;  hence,  when  the  same 
quantity  of  any  principle,  capable  of  occupying  such  vacuities,  as 
heat  may  be  supposed  to  be,  is  introduced  equally  into  both,  very 
dissimilar  apparent  eflects  must  be  produced.  The  more  porous 
body  will  absorb  and  condense  within  its  vacuities  the  added  prin- 
ciple, and  leave  but  little  external  and  sensible  ;  while  the  less 
porous  body,  having  less  room  among  its  pores,  will  exhibit  a 
larger  quantity  external  and  sensible.  The  more  porous  body, 
therefore,  may  be  said  to  have  a  greater  capacity  for  heat  than  the 
less  porous  body,  from  its  greater  power  of  absorbing  heat,  and  ren- 
dering it  latent.*  This,  we  believe,  is  the  usual  explanation  of  the 
phenomenon  under  the  assumed  circumstances,  and  it  is  probably 
correct  to  a  certain  extent :  but  there  is  obviously  another  form  of 
latent  heat,  totally  different  from  the  above,  and  which  evidently 
cannot  be  explained  on  the  same  principles,  and  this  we  have  now 
to  consider.  Let  us  suppose  that  into  a  mass  of  ice,  cooled  con- 
siderably below  the  freezing  point,  a  uniform  and  regular  flow  of 
heat  be  determined  from  some  external  source ;  the  temperature 
of  the  ice,  of  course,  will  gradually  go  on  increasing  till  it  rise  up 
to  the  freezing  point ;  it  will  then  suddenly  stop,  and  remain  sta- 
tionary till  a  quantity  of  heat,  equal  to  140  degrees  of  the  ther- 
mometer, have  flowed  into  the  ice.  The  ice  has  now  become 
water  ;  but  up  to  that  point  the  water  still  retains  the  original  tem- 
perature of  the  ice ;  after  that  point,  however,  if  the  heat  continue 

*  This  union  of  heat  with  ponderable  bodies  may,  perhaps,  be  consi- 
dered as  analog-ous  to  the  condensation  of  gaseous  bodies  by  porous  sub- 
stances— a  very  remarkable  set  of  phenomena,  which  deserve  to  be  much 
more  carefully  studied  than  they  have  been.  The  absorption  of  light  is 
probabl)^  of  a  similar  nature  ;  and  the  whole  apparently  depend  upon  che- 
mical principles,  and  probably,  if  studied  in  connexion,  would  mutually 
illustrate  each  other. 


52  CHEMISTRY. 

to  be  applied,  the  water  acquires  apparent  temperature  as  before. 
Now  in  this  experiment  a  quantity  of  heat  equal  to  140  degrees 
of  the  thermometer  has  actually  disappeared  ;  but  this  disappear- 
ance cannot  be  explained  in  the  same  manner  as  that  above  men- 
tioned ;  for  the  water,  instead  of  being  greater  in  volume,  and 
consequently  having  greater  vacuities  than  the  ice  from  which  it 
was  formed,  is  actually  less,  and  must  therefore  contain  fewer  va- 
cuities. How  then  are  the  plienomena  to  be  explained  ?  We 
commenced  our  observations  upon  heat,  by  alluding  to  the  hypo- 
thesis that  this  principle  is  capable  of  being  decomposed  into  two 
energies,  if  not  identical  Avith,  at  least  operating  in  the  same  way 
as  those  of  electricity.  In  the  above  experiment,  therefore,  we 
consider  that  the  140  degrees  of  heat  which  have  disappeared,  are 
decomposed  and  converted  into  the  two  polarizing  energies  ;  and 
that  these  energies  thus  produced  are  superadded  to  the  energies 
already  existing  attached  to  the  molecules  of  water,  and  in  this 
way  increase  their  total  quantity  or  intensity.  The  changes  in- 
duced in  the  relative  position  of  the  molecules  of  water,  by  this 
increase  of  intensity  in  their  energies,  may  be  illustrated  as  fol- 
lows : — Let  Fig.  12,  as  before,  represent 
the  position  of  two  molecules  in  the  state  of 
ice.  Here  the  similar  poles  E  E  and  e  e, 
are  of  course  mutually  repellent,  while  co- 
hesion takes  place  between  the  dissimilar 
polarities,  as  shown  in  the  figure.  Now 
suppose  the  polarities,  E  E,  e  e,  to  be  suddenly  much  increased 
in  intensity,  so  as  to  extend  beyond  the  semi-diameter  of  the 
spheres  ;  they  will  of  course  repel  each  other,  and  in  such  a  way 
that  the  two  sp.heres  will  revolve  on  the  common  axis  of  adhesion 
Mm,  and  the  axes  E  e,  E  e,  instead  of  remaining  parallel,  will 
become  at  right  angles  to  each  other,  as  in  Fig.  13  ;  or  rather  as 

FiP-  11  Fie-   14  '"  ^^^'  ^^-  ^^"  ^'?-  ^^'  ^  ^'^^^^ 

^  IS  supposed  n\  the  direction  or 

the  common  axes,  31  m  M m^ 

of  Fig  13.  in  which  view,  of 

course,  E  e,E  e,  are  supposed  to 

represent  the  chemical  axes  of 

the  two  spheres  at  right  angles  to  each  other.   Hence  in  the  liquid 

state  of  bodies  the  position  of  the  axes  of  adjoining  molecules  may 

be  supposed  to  be  at  right  angles,  or  in  some  position  less  than  right 

angles  and  approaching  parallelism.     At   exact  right  angles  the 

cohesive  polarities  are  balanced  and  neutralized,  so  that  the  points 

Afm  have  neither  a  tendency  to  unite  nor  to  separate,  but  remain 

simply  in  contact.      Hence  the  molecules  of  such  a  body  v.-ill  be 

all  disassociated  and  free  to  move  among  one  another  ;  and  if  we 

suppose  each  molecule  at  the  same  time  to  be  surrounded  by  its 


GASEOUS  FORM  OF  BODIES.  53 

atmosphere  of  caloric,  so  thin  as  not  ahogether  to  remove  mecha- 
nically the  molecules  beyond  one  another's  influence,  we  have 
probably  as  clear  an  idea  of  the  nature  of  a  liquid  as  we  are  ca- 
pable of  forming. 

Section  V. 

Of  the  Third  or  Gaseous  Form  of  Bodies. 

We  have  next  to  consider  the  most  perfect  form  of  fluidity, 
that  of  gas,  or  (adhering  to  our  former  example),  steam ;  and  we 
shall,  in  the  first  place,  take  a  short  view  of  the  molecular  arrange- 
ment of  bodies  existing  in  the  gaseous  form,  which  will  enable  us 
still  further  to  elucidate  the  subject  of  latent  heat. 

Let  us  suppose  as  before,  the  same  constant  stream  of  heat  to 
be  flowing  into  a  portion  of  water  that  we  supposed  to  be  flow- 
ing into  the  ice  :  the  w^ater  continues  to  increase  in  temperature 
and  capacity  for  heat  till  it  arrives  at  the  boiling  point ;  at  this 
moment  the  temperature  ceases  to  be  augmented,  however  much 
we  may  urge  the  apphcation  of  heat,  and  the  water  is  converted 
into  a  transparent  gas,  well  known  by  the  name  of  steam  ;  to  ef- 
fect this  latter  purpose,  however,  under  the  ordinary  circumstances 
of  atmospheric  pressure,  it  has  been  found  that  nearly  1000  de- 
grees of  heat  are  necessary,  which  large  quantity  of  heat  actually 
becomes  latent  or  disappears,  since  the  temperature  of  the  steam 
formed  never  exceeds  212°,  that  of  the  water  at  the  boiling  point. 
What  becomes  of  these  1000  degrees  of  heat  ?  We  may  suppose 
one  portion  of  it  to  become  latent  in  the  first  of  the  tw^o  ways 
described  above ;  that  is  to  say  the  water  in  the  act  of  being  con- 
verted into  vapour,  is  much  augmented  in  volume,  and  into  this 
augmented  volume,  as  into  a  sort  of  vacuum,  a  portion  of  the  heat 
may  be  supposed  to  rush  and  become  insensible  ;  but  another  por- 
tion of  heat  is  obviously  decomposed,  and  goes  to  augment  the 
molecular  polarities  of  the  water,  which,  in  the  case  of  steam 
(and  in  all  gases),  may  be  imagined  to  be  arranged  in  some  such 
way  as  the  following  : — 

In  Fig.  15,  we  have  represented  as  before, 
''^'      '  though  in  a  different  manner,  the  chemical 

axes  at  right  angles  to  each  other ;  at  which 
angle  the  cohesive    polarities  are  balanced 
and  neutralized.     This  angle,  therefore,  may 
^^     -.^g^  1^^  considered  as  the  point  at  which  liquidity 

terminates  and  perfect  fluidity  begins.  The  next  augmentation  of 
heat  increases  the  chemical  polaric  intensities  still  further,  so  as 
to  induce  them  to  repel  (or  rather  to  attract)  each  other's  axes  into 

5* 


54  CHEMISTRY. 

the  parallel  position,  Fig.  16;  where  the 
chemical  polarities  are  quite  reversed,  and 
of  course,  the  contiguous  cohesive  polari- 
ties m  and  m  are  brought  into  the  maxi- 
mum state  of  repulsion.  Now  such  position, 
or  some  angle  greater  than  a  right  angle, 
may  be  supposed  to  be  that  assumed  by  the  chemical  axes  of  the 
molecules  of  all  bodies  when  in  the  gaseous  state.  Hence,  as 
there  are  two  kinds  of  attraction,  so  there  must  likewise  be  two 
kinds  of  repulsion,  viz.  heterogeneous  or  chemical  repulsion ; 
and  homogeneous,  or  self-repulsion,  opposed  to  cohesion,  upon 
which  the  gaseous  form  of  bodies  principally  depends. 

But  here  a  question  arises  :  in  what  state  are  the  molecules  of 
bodies  in  the  condition  of  vapour,  as  those  of  water  at  all  tempe- 
ratures below  212°  ;  for  instance  at  32°  ?  According  to  an  hy- 
pothesis to  be  presently  mentioned,  a  given  volume  of  steam,  at 
212°,  contains  the  same  number  of  self-repulsive  molecules  as  a 
similar  volume  of  air  under  the  same  temperature  and  pressure, 
and  therefore  has  the  same  elasticity.  But  the  elasticity  of  the 
vapour  of  water  at  32°  is  only  equal  to  about  l-5th  of  an  inch  of 
mercury  ;*  hence  the  same  given  volume  of  that  vapour  at  32° 
will  only  weigh  about  1-1 50th  of  what  steam  ought  to  weigh,  sup- 
posing it  could  exist  as  a  permanent  gas  at  32°,  and  under  a  pres- 
sure of  thirty  inches  of  mercury.  The  molecules  of  the  vapour, 
consequently,  will  be  five  or  six  times  further  apart  than  in  per- 
fectly gaseous  bodies  under  a  similar  temperature  and  pressure.! 
Let  us  now,  in  the  last  place,  inquire  how  the  above  supposi- 
tions respecting  gaseous  bodies  accord  wilii  their  common  leading 
properties,  viz.,  with  their  self-repulsive  or  diffusive  properties  ; 
their  equable  expansion  by  heat  ;  their  increase  in  volume  in  the 
inverse  proportion  of  the  force  with  which  they  are  compressed; 
and  with  their  similar  capacities  for  heat. 

*  Tl)e  elastic  force  of  vajiours  increases  with  their  temperatures  ;  that 
is  to  say,  accordhig-  to  oui- h}  polhesis,  increases  with  the  angle  formed  by 
the  chemical  axes  of  their  molecules.  At  exact  rij^ht  ansjles  the  elastic 
force  is  0 ;  at  180°  it  is  equal  to  that  of  air  under  similar  pressure  and  tem- 
perature. Hence  all  intermediate  elasticities  lie  between  these  two  points. 

f  Supposing'  ii  were  possible  for  steam  to  exist  at  32°,  of  course  at  this 
temperature  its  weiglit  would  bear  to  thtit  of  air,  the  same  proportion  it 
bears  at  212°,  that  is  to  sa}',  as  5  to  8.  Hence  100  cubic  inches  of  steam 
at  32°,  ought  to  weig-h  20.49375  grains  ;  or  5-8ths  of  32-79  grains,  which 
is  the  weight  of  100  cubic  inches  of  air  at  32°.  But  the  Aveight  of  100 
cubic  inches  of  steam  at  32°  is  only  .13C6  grain,  or  l-150ththat  of  air.  Ti;e 
number  of  molecules  in  steam  at  32°  is  consequently  only  l-150th  of  those 
in  air  at  32°.  Hence  this  diminution  of  the  number  of  molecules,  if  we 
suppose  them  to  be  diffused  equally  throughout  the  same  space  of  100 
cubic  inches,  must  of  coin-sc,  as  stated  in  tlie  text,  cause  them  to  be  be- 
tween five  and  six  times  further  apart. 


PROPERTIES  OF  GASES.  55 

Of  the  diffusion  of  Gaseous  Bodies. — For  the  facts  connected 
with  this  most  important  subject  we  are  principally  indebted  to 
Dr.  Daltoa  and  to  Mr.  Graham  ;  the  latter  of  whom  has  shown 
that  when  any  gas  or  air  is  confined  in  a  vessel  furnished  with  a 
very  narrow  aperture  or  with  a  porous  plug,  an  interchange  between 
the  confined  and  the  external  airs  immediately  begins  to  take  place 
through  the  communicating  aperture  ;  and  that  this  interchange 
continues  to  go  on  to  a  certain  point,  which,  with  respect  to  the 
same  gas,  appears  to  be  uniform,  but  differs  in  difl'erent  gases  ac- 
cording to  a  certain  law.  Two  gases  also,  whatever  may  be  their 
specific  gravities,  and  however  they  may  be  introduced  into  the 
same  vessel,  speedily  become  mixed  uniformly  throughout.  These 
facts  evidently  indicate  a  species  of  self-repulsive  influence  among 
the  molecules  of  the  same  gas,  which  appears  to  be  satisfactorily 
accounted  for  by  our  hypothesis.  The  argument  is  very  simple 
and  obvious  :  Two  molecules  of  the  same  matter  have  a  tendency 
to  cohere  and  to  form  a  solid,  when  the  chemical  polarities  of 
these  molecules  are  similarly  arranged,  and  do  not  extend  beyond 
the  semi-diameters  of  the  molecules  ;  but  two  molecules  of  differ- 
ent matter,  under  circumstances  precisely  alike,  remain  passive, 
and  have  no  tendency  to  cohere.  Hence,  while  two  molecules 
of  the  same  matter,  having  the  intensity  of  their  polarities  much 
increased,  and  their  chemical  poles,  consequently,  reversed,  repel 
each  other,  or  become  se^-repulsive  ;  two  molecules  of  different 
matter,  still  retaining  their  mutual  passiveuess,  do  not  repel  each 
other. 

There  is  reason  to  believe  that  these  phenomena  are  not  con- 
fined to  bodies  perfectly  gaseous,  but  exist  also  in  that  less  per- 
fect gaseous  condition  termed  vapour,  of  which  the  vapour  of 
water  may  be  considered  as  the  most  familiar  example.  On  this 
supposition,  and  particularly  that  the  above  law  of  diffusion  holds 
among  vapours,  (which  is  probably  the  case,  though  in  a  modified 
form)  the  lower  the  specific  gravity  of  the  vapour,  that  is  to  say 
the  lower  the  temperature,  the  greater  the  diffusive  power ;  and 
consequently  the  more  rapid  the  evaporation  :  a  most  important 
inference  that  will  enable  us  to  explain  many  meteorological  phe- 
nomena at  present  quite  inexplicable.  Something  very  similar, 
if  not  identical  with  the  above  phenomena,  also  exists  in  liquids 
and  perhaps  in  solids.  Thus  the  molecules  of  certain  matters  dif- 
fused through  a  liquid,  as  water,  may  be  supposed  to  exert  in  some 
cases  a  self-repulsive  influence  on  each  other,  by  which  supposi- 
tion only  do  their  equal  diffusion  through  a  large  mass  of  liquid 
seem  explicable.  Even  in  the  solid  slate,  as  above  observed,  some- 
thing of  the  kind  appears  to  exist,  especially  among  organized 
bodies,  which  apparently  owe  some  of  their  most  remarkable  pro- 


56  CHEMISTRY. 

perties  to  the  diffusion  of  active  self-repulsive  molecules  through- 
out their  substance. 

Of  the  equal  Expansion  of  Gaseous  Bodies  by  Heat. — With 
respect  to  the  second  important  property  of  gaseous  bodies,  that 
under  the  same  temperature  and  pressure  they  all  undergo  equal 
expansion  by  an  equal  increase  of  lieat ;  this  seems  to  be  expli- 
cable only  on  the  supposition  that  all  gaseous  bodies,  lender  the 
same  pressure  and  temperature,  contain  equal  numbers  of  self- 
repulsive  molecules :  a  most  important  conclusion,  as  we  shall  see 
hereafter,  and  one,  which  at  present  we  are  anxious  a  little  further 
to  illustrate.  Supposing  the  fact  to  be,  as  it  is,  undeniable,  that 
within  the  ordinary  limits  of  experiment,  all  perfectly  gaseous 
bodies  expand  equally  by  similar  increments  of  heat,  z/' different 
gases  contain  unequal  iwixnhe^is,  of  self-repulsive  molecules,  those 
gases  which  contain  the  least  number  of  molecules,  must  exert 
the  greatest  power,  and  consequently  have  the  greatest  disposition 
to  expand;  in  other  words,  the  expansive  power  of  the  molecules 
of  a  gas,  must  increase  as  their  number  diminishes  ;  and  not  only 
so,  but  in  order  to  produce  the  effect  stated,  the  expansive  power 
must  increase,  neither  more  nor  less,  but  exactly  as  the  number 
diminishes — a  law  which  when  applied  to  extreme  cases  becomes 
obviously  absurd.  Further  it  may  be  observed,  in  corroboration 
of  the  hypothesis  advanced,  that  in  the  gaseous  state  the  molecules 
of  bodies  may  be  considered  as  having  undergone  the  utmost  ef- 
fects, that  any  increase  of  heat  can  produce  upon  them.  All  their 
interstitial  vacuities  may  be  supposed  to  be  already  saturated  with 
it;  while  an  atmosphere  may  be  supposed  to  surround  each  mole- 
cule, keeping  them  individually  at  a  considerable  distance  from 
each  other  :  their  polarities  also  may  be  supposed  to  have  under- 
gone their  ultimate  change,  so  that  no  more  heat  can  be  rendered 
latent  by  inducing  further  changes,  except  in  degree,  which  degree 
may  be  supposed  to  be  common  to  all  gases.  Hence  every  mole- 
cule of  matter,  when  in  the  gaseous  state,  and  subjected  to  similar 
pressure  and  temperature,  may,  without  reference  to  its  other  pro- 
perties, be  supposed  to  be  in  circumstances  exactly  similar,  and 
consequently  liable  to  be  affected  in  an  exactly  similar  manner  by 
all  further  increments  of  heat. 

Of  the  inverse  Relation  of  the  J\ilume  to  the  Compressive 
lorce. — Nearly  the  same  remarks  apply  to  this  law  as  to  the  pre- 
ceiling;  for  were  the  numbers  of  molecules  in  each  gas  supposed 
to  be  unequal,  the  diminution  of  volume  under  similar  pressure 
ought  to  vary  also,  which  is  not  the  case,  at  least  in  the  more  per- 
fect gaseous  bodies,  and  neither  this  observation,  nor  those  in  the 
former  para<rraph  apply  to  vapours. 

Of  the  similar  capacity  of  Gaseous  Bodies  for  Heat. — The 
begt  experiments  seem  to  show  that  under  the  same  pressure  the 


HEAT  IN  MOTION.  57 

same  volumes  of  all  gases  have  ihe  same  capacity  for  heat — a  cir- 
cumstance quite  according  with  the  other  phenomena.  Hence, 
for  the  above  and  other  reasons  which  might  be  mentioned,  we 
have  been  induced  to  adopt  the  hypothesis  already  stated,  that, 
tinder  the  same  pressure  and  temperature,  all  bodies  in  a  per- 
fectly gaseous  state  contain  equal  iiuinbers  of  self-repulsive  mo- 
lecules.^ 

Section  VI. 

Other  Properties  of  Heat.     Of  Heat  in  Motion. 

Heat  appears  to  be  in  a  constant  state  of  motion  and  of  inter- 
change between  different  bodies,  among  which  it  finally  settles 
into  a  state  of  equilibrium.  If  accumulated  in  any  body,  this  ac- 
cumulation cannot  be  preserved  ;  but  the  excess  will  fly  off  in 
spite  of  all  we  can  do  to  the  contrary,  and  sooner  or  later  the  equi- 
librium will  be  restored.  This  motion  of  heat  takes  place  in  three 
ways,  which  a  common  fire-place  very  well  illustrates.  If,  for 
instance,  we  place  a  thermometer  directly  before  a  fire,  it  soon 
begins  to  rise,  indicating  an  increase  of  temperature.  In  this  case 
the  heat  has  made  its  way  through  the  space  between  the  fire  and 
the  thermometer,  by  the  process  termed  radiation.  If  we  place 
a  second  thermometer  in  contact  with  any  part  of  the  grate,  and 
awav  from  the  direct  influence  of  the  fire,  we  shall  find  that  this 
thermometer  also  denotes  an  increase  of  temperature  ;  but  here  the 
heat  must  have  travelled  through  the  metal  of  the  grate,  by  what 
is  iexmeA  conduction.  Lastly,  a  third  thermometer  placed  in  the 
chimney,  away  from  the  direct  influence  of  the  fire,  will  also  in- 
dicate a  considerable  increase  of  temperature  ;  in  this  case  a  por- 
tion of  the  air,  passing  through  and  near  the  fire,  has  become 
heated,  and  has  carried  up  the  chimney  the  temperature  acquired 
from  the  fire.  There  is  at  present  no  single  term  in  our  language 
employed  to  denote  this  third  mode  of  the  propagation  of  heat ; 
but  we  venture  to  propose  for  that  purpose,  the  term  convection,'^ 

•  It  is  proper  to  observe  tliat  these  views  were  adopted  by  the  author 
long'  before  he  was  aware  of  the  existence  of  the  essays  on  the  subject  by 
Messrs.  Avog-adro,  Ampere,  and  Dumas.  Indeed  he  was  unacquainted 
with  those  of  Dumas,  which  most  nearly  resemble  his  own,  till  he  saw  them 
alluded  to  in  Mr.  Johnston's  recent  report  on  chemistry  in  the  Transactions 
of  tlie  British  Association.  Mr.  Donovan  seems  to  consider  the  above  hy- 
pothesis as  untenable  ;  but  we  think  his  arguments  entirely  inconclusive. 
See  Giornale  di  Fisica,  sec.  ii.  tom.  viii.  p  1. ;  Annates  de  Chimie,  torn, 
xc.  p.  43  ;  a  Treatise  on  Chemistry,  by  Mr.  Donovan,  in  Lardner's  Cabinet 
Cyclopaedia,  p.  379  ;  and  the  Introduction  to  Dumas's  Traite  de  Chimie 
appliquee  aux  Arts,  which  excellent  work  the  author  had  been  prevented 
from  perusing  by  the  nature  of  the  title. 

f  Convedio,  a  carrying  or  conveying. 


58  CHEMISTRY. 

which  not  only  expresses  the  leading  fact,  but  also  accords  very 
well  with  the  two  other  terms.  Each  of  tliese  modes  of  the  pro- 
pagation of  heat  possesses  certain  peculiarities,  on  which  we  pro- 
ceed to  make  a  few  remarks. 

Radiation  of  Heat. — Heat  radiates  in  vacuo  in  all  directions 
equally,  and  with  immeasurable  velocity.  Heat  radiates  also  through 
all  gaseous  bodies,  and  more  or  less  through  transparent  media. 
Radiation  goes  on  at  all  temperatures  ;  but  the  quantity  of  heat 
radiated  in  a  given  time  bears  some  proportion  to  the  excess  of 
the  temperature  of  the  radiating  body  a'30ve  that  of  the  surround- 
ing medium.  Radiant  heat  is  capable  of  being  rejected  like  light, 
(to  be  presently  noticed,)  and,  indeed,  obeys  altogether  somewhat 
similar  laws.  Those  surfaces,  however,  that  reflect  light  most 
perfectly,  are  not  equally  adapted  to  the  reflection  of  heat.  Metals 
in  general,  and  particularly  when  highly  polished,  are  the  best 
reflectors  of  heat,  while  glass,  which  reflects  light  most  perfectly, 
reflects  comparatively  little  heat;  thus  tin-plate  reflects  about  eight 
times  as  much  heat  as  a  glass  mirror.  The  radiation  of  heat  is 
much  influenced  by  the  nature  and  state  of  the  surfaces  of  bodies. 
Thus  a  surface  coated  with  lamp-black  radiates  eight  or  nine  times 
as  much  heat  as  a  polished  surface  of  tin  or  silver;  and  in  general 
polished  surfaces,  particularly  of  metal,  radiate  much  less  than 
other  surfaces.  As  might  be  expected,  this  diflTerence  of  radiating 
power  exerts  great  influence  in  the  cooling  of  bodies  ;  thus  warm 
water  retains  its  heat  much  longer  in  a  bright  tin  vessel,  than  in 
the  same  vessel  coated  with  linen,  paint,  or  particularly  lamp-black. 
Radiant  heat  is  absorbed  with  different  facilities  by  difTerent  sur- 
faces. The  absorbing  power  of  surfaces  seems,  indeed,  to  vary 
directly  as  their  radiating  power,  and  inversely  as  their  reflecting 
power.  That  is  to  say,  surfaces  receive  heat  by  radiation  nearly 
with  the  same  degree  of  facility  as  they  give  it  off;  while  those 
that  reflect  most,  of  course,  must  absorb  least ;  a  surface  covered 
with  lamp-black,  for  example,  receives  in  a  given  time  eight  or 
nine  times  as  much  heat  by  radiation  as  a  polished  tin  surface  re- 
ceives. From  these  remarks,  it  will  be  readily  inferred,  that  the 
colours  of  bodies  may  have  considerable  influence  in  the  radiation 
and  absorption  of  heat;  now  this  is  found  to  be  the  case, "and  the 
darker  tlie  colour  of  a  body,  the  more  readily  it  gives  off,  and  ab- 
sorbs radiant  heat.  Radiant  heat  has  the  power  of  passing  through 
transparent  bodies,  as  glass.  This  power,  however,  varies  accord- 
ing to  the  thickness  of  the  glass,  its  relative  position  to  the  radia- 
ting body,  and  a  variety  of  other  circumstances  not  well  under- 
stood ;  but  generally  speaking  heat  seems  to  obey  laws,  more  or 
less,  analogous  to  those  of  light  under  similar  circumstances. 
Conduction  of  Heat. — The  conduction  of  heat  is  chiefly  con- 


OF  LIGHT.  59 

fined  to  solid  bodies  ;  and  as  solids  exist  of  every  degree  of  con- 
sistency and  density,  from  perfect  fluidity  up  to  perfect  hardness, 
the  conducting  power  varies  in  like  manner.  Hence  the  laws  of 
conduction  and  those  of  radiation  have  a  mutual  dependance  ;  and, 
in  fact,  the  laws  of  conduction  may  be  considered  as  only  extreme 
cases  of  the  laws  of  radiation.  The  conduction  of  heat  through 
bodies  seems  to  take  place  equally  in  all  directions.  In  general 
the  densest  bodies,  as  metals,  stones,  hard  woods,  &c.,  have  the 
greatest  conducting  power,  though  these  differ  exceedingly  among 
one  another.  Porous  bodies  in  general  are  bad  conductors ;  and 
of  such  bodies  charcoal  may  be  considered  as  one  of  the  worst 
conductors.  Among  substances  employed  as  articles  of  dress, 
hare's  fur  and  eider  down  are  the  worst  conductors,  and  flax  the 
best.  The  relative  conducting  powers  of  substances  of  this  class 
seem  to  depend  much  upon  the  quantity  of  air  enclosed  within 
their  interstices,  and  the  power  of  attraction  by  which  this  air  is 
retained  or  confined.  The  conducting  power  of  liquids  and  of 
gases  is  very  limited,  though  under  certain  circumstances  they  ajo- 
pear  to  possess  this  power  in  a  high  degree.  But  this  power  is 
only  apparent,  and  heat  is  chiefly  communicated  through  liquids, 
and  also  through  gases  by  the  third  process  above  alluded  to,  viz. 
convection.  By  convection  however,  heat  is  only  propagated  in 
one  direction,  namely,  upwards  ;  hence  almost  any  degree  of  heat 
may  be  applied  to  the  upper  surface  of  a  liquid  or  gas  without 
aflfecting  the  lower. 

Such  are  the  principal  phenomena  connected  with  the  motion 
of  heat ;  but  before  we  proceed  to  speak  of  the  sources  of  this 
wonderful  agent,  we  have  yet  to  consider  another  imponderable 
principle  of  the  utmost  importance,  and  intimately  connected  with 
heat ;  viz.,  Light, 

Section  VII. 

Of  Light, 

The  laws  of  the  motion  of  light,  of  its  reflection,  refraction, 
polarization,  (fee,  properly  belong  to  another  department ;  we 
shall,  therefore,  only  briefly  describe  them  here,  and  endeavour 
to  point  out  the  general  connexion  and  analogy  they  bear  to  the 
phenomena  of  chemistry,  and  more  especially  to  the  phenomena 
of  heat  and  electricity. 

Radiation  or  Motion  of  Light. — Light  radiates  or  moves  in 
straight  lines  with  such  inconceivable  velocity,  that  it  occupies  only 
about  eight  minutes  in  travelling  from  the  sun  to  our  earth,  so 
that  it  must  move  at  the  rate  of  nearly  200,000  miles  in  a  second  ! 
At  the  same  rate  it  would  occupy  about  four  hours  to  travel  to  us 


60 


CHEMISTRY. 


from  Ihe  planet  Uranus,  the  present  ultima  Tlnde  of  our  system  ; 
hence  if  this  planet  were  at  any  given  instant  suddenly  annihilated, 
we  should  not  miss  it  for  four  hours  afterwards  ;  and  when  we 
look  at  it,  we  do  not  see  it  where  it  actually  is  at  this  instant,  but 
where  it  was  four  hours  previously.  A  cannon  ball,  when  first 
shot  from  the  cannon,  moves  with  a  velocity  of  between  2000 
and  3000  feet  per  second  ;  supposing-,  therefore,  it  could  retain  its 
initial  velocity,  it  would  scarcely  move  in  a  year  as  much  as  light 
moves  in  a  single  second  !  The  utmost  velocities  of  the  earth  and 
other  planets,  in  their  orbits  or  on  their  axes,  scarcely  exceed 
30  or  40  miles  in  a  second.  Hence  the  utmost  velocity  that  we 
are  acquainted  with  as  possessed  by  ordinary  matter,  and  therefore 
the  utmost  perhaps  of  which  such  matter  is  capable,  only  amounts 
to  the  l-5000th  or  l-6000lh  of  that  of  light!  These  striking  facts 
are  mentioned  with  the  view  of  conveying  some  notion  of  the  im- 
mensity of  space,  and  of  the  wonderful  velocity  with  which  it  is 
in  every  direction  penetrated  by  light.  They  seem  also  to  show, 
that  if  light  be  matter,  it  must  exist  in  a  state  of  tenuity,  totally 
diflierent  from  the  ponderable  matter  we  are  acquainted  with, 
which  actually  seems  incapable  of  such  velocity.* 

If  we  consider  heat  and  light  to  consist  of  polarized  molecules 
in  the  self-repulsive  state,  and  to  obey  the  same  laws  that  ponde- 
rable matters  in  the  gaseous  state  obey,  which  is  exceedingly 
probable  ;  the  radiation  of  these  imponderable  bodies  will  be  ana- 
logous to  the  diflusion  of  gaseous  bodies,  and  by  knowing  their 
velocity  and  applying  the  same  law,  we  may  deduce  their 
comparative  gravities. 

Hfflection  and  Refraction  of  Light. — In  free  space,  as  before 
observed,  light  moves  in  straight  lines;  but  when  a  ray,  7?,  Fig. 


Fig.  17. 


17,  falls  upon  a  polished 
surface,  as  of  glass,  a  portion 
of  it  is  reflected  in  the  direc- 
tion e  E,  and  the  angle,  R  e 
P,  called  the  angle  of  inci- 
dence, is  always  equal  to  the 
angle,  P  e  £,  called  the 
angle  of  reflection.  Another 
portion,  e  m,  passes  through 
the  glass,  but  instead  of  con- 
tinuing to  move  in  the  same 
straight  line,  is  bent  consi- 
derably out  of  that  direction 
towards  the  perpendicular  P 


Pouillet,  Elemcns  de  Physique  et  de  Meteorolog-'ie  torn.  iii.  p.  216. 


POLARIZATION  OF  LIGHT. 


61 


Q ;  it  then  makes  its  exit  at  m,  and  goes  on  in  the  direction  m  ikf, 
parallel  to  its  original  direction,  Re.  This  portion  of  the  ray  is 
said  to  have  undergone  refraction  ;  a  term  indicating  that  its  na- 
tural course  has  been  broken.  Such  are  the  general  facts  ;  and 
the  study  of  their  laws,  varieties,  and  peculiarities,  as  modified 
by  different  media,  constitutes  the  science  of  optics,  a  branch  of 
knowledge  not  f;illing  within  our  present  design.  In  connection 
with  this  part  of  our  subject,  it  only  remains  to  observe,  that  in 
passing  through  the  most  transparent  bodies  much  light  is  lost, 
by  absorption  and  in  other  ways.  So  also  when  light  falls  upon 
metallic  bodies,  such  as  polished  silver,  about  one-half  only  is 
reflected,  while  the  other  half  is  absorbed  and  lost.  Different 
substances,  however,  differ  materially  in  these  respects,  and  from 
the  experiments  of  M.  Bouguer  and  M.  Lambert,  it  appears  that 
in  fluids,  transparent  solids  and  metals,  the  quantity  of  light  re- 
flected, increases  with  the  angle  of  incidence  reckoned  from  the 
perpendicular  ;  whereas  in  white  opaque  bodies  the  quantity  of 
light  reflected,  decreases  with  the  angle  of  incidence.*  We  shall 
hereafter  have  occasion  to  revert  to  these  curious  facts. 

Polarization   of  Light. — The    next   property   we    have    to 
notice  is  what  is  called  the  polarization  of  light.     Let  us  sup- 
ply. iq  ,,  poseFig.  18,torepre- 
^'^•  ■^^-             ^  sent  a  bundle  of  plates 

of  thin  window-glass, 
bound  together  in  the 
manner  indicated.  Let 
^  e  be  a  ray  of  light 
falling  on  the  upper 
plate,  at  an  angle 
of  incidence  of  about 
56°  ;  a  portion  of  the 
ray  will  be  reflected, 
and  will  move  in  the 
direction  e  JS,  while 
another  portion  of  the 
ray  e  m,  will  pass  through  the  bundle  of  glass  plates  onwards  to 
M,  according  to  the  laws  of  reflection  and  refraction  already  stated. 
Now  these  two  rays  e  E  and  m  M,  possess  remarkable  properties, 
similar  to  one  another  in  most  respects,  but  directly  opposed 
in  another.  Of  these  properties  we  shall  endeavour  to  give  a 
general  idea. 


•  See  article  Optics,  p.  67,  and  68,  in  the  Library  of  Useful  Knowledge. 
Where  the  orig-inal  observations  are  to  be  found,  which  are  there  referred 
to,  we  do  not  at  present  know. 

6 


62  CHEMISTRY. 

If  the  ray  of  light  R  Jl^  after  failing  upon  the  vertical  glass  A^ 
Fig.  19,  at  an  angle  of  incidence  of  56°,  be  received  on  a  plate 

Fig.  19. 


of  glass,  C,  placed  at  the  same  angle  of  incidence,  and  be  then 
reflected  from  C  to  E ;  in  the  position  intended  to  be  shown  in 
the  figure,  when  the  ray  B  is  first  reflected  in  a  horizontal  plane, 
R  A  C,  and  then  in  a  vertical  plane,  ACE,  the  ray  C  E  be- 
comes so  weak  as  to  be  scarcely  visible,  the  whole  of  it  having 
passed  through  the  glass  C.     But  if  the  glass  C  be  turned  round 
90°,  (the  ray  A  C  being  supposed  to  be  the  axis  of  motion)  so 
that  the  ray  C  E  he  reflected  horizontally ;   instead  of  passing 
through  the  glass  C  as  before,  the  whole  of  the  ray  C  E  will  be 
reflected.  If  we  continue  to  turn  the  plate  Cupon  the  axis  A  C,  round 
the  entire  circle,  these  alternations  of  transmission  and  reflection  will 
be  found  to  take  place  in  the  same  manner  at  the  two  other  quadrants 
180°  and  270°.   Hence  the  xzj  RA,  by  reflection,  has  acquired  pro- 
perties altogether  new ;  it  is  said  in  short,  to  have  acquired  polarity, 
or  to  have  become  polarized.    Now  recurring  to  Fig.  18,  the  ray 
R  e,  in  that  figure  will  of  course  follow  the  same  laws  as  the  ray 
R  A  in  Fig.  19,  that  is  to  say,  the  ray  e  E  will  have  acquired 
polarity  by  reflection.     Let  us  now  consider  what  has  happened 
to  the  refracted  ray  m  31  m  the  same  Fig.  18.     This  ray  m  M 
will  also  be  found  to  be  polarized  ;  but  if  we  receive  it  on  a  glass 
plate,  F  G,  at  the  polarizing  angle  of  56°,  we  shall  find  that  it 
will  refuse  to  be  reflected  ;  whereas  the  reflected  ray  e  E  does 
not  refuse  to  be  again  reflected,  unless  the  plate  E  G  he  turned 
round  90°,  or  into  a  plane  at  right  angles  to  that  plane  in  which 
the  refracted  ray  m  Af  had  refused  to  be  reflected.     Hence  we 
conclude  that  when  a  ray  of  light  is  incident  at  the  polarizing 
angle  upon  a  transparent  body,  the  whole  of  the  reflected  light  is 
polarized  ;  while  the  whole  of  the  transmitted  light  is  also  polar- 
ized, but  in  a  plane  at  right  angles  to  that  in  which  the  reflected 
ray  is  polarized. 

Such  is  the  general  law,  and  it  may  not  be   amiss  to  allude 
briefly  to  another  familiar  illustration  of  it.     Every  one  is   ac- 


DECOMPOSITION  OF  LIGHT. 


63 


quainted  with  the  mineral  called  Iceland  spar,  and  with  the  sin- 
gular property  which  this  mineral  possesses  of  forming  a  double 
image  of  objects  seen  through  it,  or  its  property  of  double  refrac- 
tion ;  that  is  to  say  when  a  ray  of  light  falls  on  a  crystal  of  such 
spar  in  a  particular  direction,  the  ray  is  separated  into  two.  Now 
it  is  a  remarkable  fact  that  if  these  two  rays  be  examined  in  the 
way  before  directed,  when  speaking  of  reflected  and  transmitted 
light,  it  will  be  found  that  both  are  polarized,  but  that  the  two 
rays  are  polarized  in  planes  at  right  angles  to  each  other  ;  that  is 
to  say,  the  ordinary  transmitted  ray  is  polarized  like  the  ordi- 
nary ray  transmitted,  through  the  bundle  of  glass  plates  ;  while 
the  extraordinary  transmitted  ray  is  polarized  like  the  ray  re- 
flected from  these  plates.  Many  bodies  are  similarly  constituted  ; 
while  others  have  two  or  more  planes  or  axes  of  double  refrac- 
tion, giving  origin  to  a  variety  of  curious  and  beautiful  properties, 
which  it  would  be  quite  foreign  to  our  present  purpose  to  detail 
further. 

Decomposition  of  light. — When  a  ray  of  light,  R^  Fig.  20, 
traverses  a  prism,  CD  F,  instead  of  passing  onward  in  the  direc- 

Fig.  20. 


Violet 

Indigo 

Blue 

Orecn 

Yellow 

Orange 

Red 


White 


X.' 
O'- 


tion  Y,  it  is  refracted  into  the  spectrum  E  e;  which  spectrum 
when  received  upon  the  screen,  A  B,  will  be  found  to  consist  of 
seven  different  colours,  in  the  order  and  of  the  kind  described, 
each  having,  of  course,  different  refractive  powers  ;  the  red  being 
the  least,  and  the  violet  the  most  refracted  from  the  original  direc- 
tion R  y,  of  the  solar  beam.  This  oblong  image  is  called  the 
solar,  or  sometimes,  the  prismatic  spectrum,  and  Sir  Isaac  New- 
ton found  that  each  colour  consists  of  light  no  longer  separable, 
like  white  light,  into  others,  but  having  uniform  refractive  pro- 
perties :  hence  he  called  all  the  seven  colours  simple  or  homo- 
geneous, in  opposition  to  white  light,  which  he  called  compound 
or  heterogeneous.*     This  important  fact  presents  a  clue  to,  and 

*  Sir  David  Brewster  has  lately  shown  that  there  are,  in  fact,  but  three 
simple  colours,  the  redf  the  yellow  and  the  blue,  and  that  each  of  these 


64  CHEMISTRY. 

exhibits  the  general  law  which  regulates  the  endless  variety  and 
change  of  colours  ;  as  bodies  appear  to  have  this  or  that  colour, 
according  as  they  have  the  power  of  reflecting  or  transmitting 
this  or  that  colour,  and  of  absorbing  or  reflecting  the  rest ;  while 
wliite  bodies  reflect  all,  and  black  absorb  all.  Besides  colour, 
it  has  been  likewise  noticed  that  different  portions  of  the  prismatic 
spectrum  possesses  difl^erent  heutimi;  and  chemical  or  electrical 
properties.  These  vary  in  some  respects,  according  to  the  na- 
ture of  the  prism  employed.  In  general  the  heating  power  in- 
creases towards  the  red  ray  ;  while  the  chemical  power  seems  to 
be  regulated  in  some  degree  by  the  nature  of  the  colour,  but  is 
greater  (though  of  opposite  character)  at  the  two  extremities  than 
in  the  centre  of  the  spectrum,  where  it  appears  to  be  nearly  null. 
The  chemical  properties  of  light,  however,  are  by  no  means 
well  understood,  and  have  not  received  the  attention  which  they 
merit. 

Upon  an  attentive  consideration  of  the  phenomena  of  heat  and 
of  light,  and  a  careful  comparison  of  them  with  the  general  phe- 
nomena of  polarizing  forces,  it  is  impossible  not  to  be  struck  with 
the  close  analogy  tliat  prevails  throughout  the  whole.  The  phe- 
nomena of  heat  have  hitherto  been  very  imperfectly  studied,  and 
in  consequence  we  are  much  less  able  to  trace  the  analogy ;  but 
the  phenomena  of  light  from  their  obvious  and  striking  characters 
have  attracted  more  attention,  are  much  better  understood.  To 
enter  further  upon  the  inquiry  here  would  be  quite  foreign  to 
the  object  of  this  treatise  ;  we  cannot  however,  in  concluding 
these  remarks,  refrain  from  repeating  an  opinion  already  express- 
ed, that  the  molecules  both  of  heat  and  of  light  possess  polari- 
ties precisely  similar  to  those  of  ponderable  bodies  ;  and  that  not 
only  the  chemical  agencies  of  these  principles,  but  those  pheno- 
mena of  light  also  at  present  so  beautifully  illustrated  l3y  the 
hypothesis  of  undulse,  will  be  hereafter  found  to  admit  of  explana- 
tion on  the  more  probable  supposition  of  molecular  polarity.! 

colours  exists  throughout  the  spectrum.  Hence,  probably,  like  the  dif- 
ferent electric  and  mae^'netic  cnerg'ies,  these  elementary  colours,  or,  at 
least,  the  red  and  the  blue  (tlie  yellow  being  probably  merely  resultant), 
can  never  be  entirely  sepai'ated  from  eacli  otlier. 

+  In  the  Newtonian  hypothesis  of  Jits  of  easy  transmission  and  of  easy 
rejlectiony  the  molecules  of  light  may  be  regarded  as  little  magnets  re- 
volving rapidly  round  their  centres  \\'hile  tliey  advance  in  their  course, 
and  thus  presenting  alternately  their  attractive  and  repulsive  poles.  (See 
Discourse  on  the  Study  of  Natural  Philosophy,  by  Sir  J.  Ilerschel,  p.  253.) 
In  our  hypothesis,  tlie  chemical  poles  of  all  self-repvdsive  molecules  are 
supposed  to  be  ari-angcd  positive  and  negative  alternately  ;  (see  Fig.  16, 
page  54)  by  which  arrangement  the  contiguous  cohesive  polarities  are 
rendered  of  the  same  kind,  and  consequently  repulsive.  Hence  when  a 
scries  of  self-repulsive  molecules  move  onwards  in  virtue  of  their  self-re- 


OF  THE  SOURCES  OF  HEAT  AND  LIGHT.  65 


Section    VIII. 

Of  the  Sources  of  Heat  and  Light. 

The  principal  and  obvious  sources  of  heat  and  light  are  the 
sun,  electricity,  mechanical  action  ;  change  of  physical  con- 
dition, change  of  chemical  condition  ;  and  organic  action. 

The  sun  is  the  most  obvious  and  unvarying  source  from  which 
both  heat  and  light  are  communicated  to  our  earth.  The  nature 
of  the  sun,  however,  and  the  mode  in  which  that  wonderful  sup- 
ply of  heat  and  light  is  maintained  are  quite  unknown  to  us,  and 
will  probably  always  remain  so.  Electricity  is  another  source 
of  heat  and  light  which  are  developed  at  the  moment  of  the  equi- 
librium of  the  two  energies  ;  and  some  of  the  most  intense  de- 
grees of  heat  and  light  that  have  been  produced  have  sprung  from 
a  galvanic  apparatus.  The  sudden  condensation  of  air  is  likewise 
a  source  from  which  heat  and  light  are  often  both  extricated,  on 
principles  that  it  will  not  perhaps  be  difficult  to  understand  from 
what  has  been  stated.  The  extrication  of  heat  by  percussion  and 
condensation  appear  to  be  limited,  but  its  extrication  by  friction 
seems  to  be  boundless  ;  that  is  to  say,  so  long  as  friction  is  kept 
up,  will  heat  continue  to  be  extricated,  but  whence  the  heat  is 
derived  does  not  appear  to  be  capable  of  satisfactory  explanation, 
unless  we  suppose  a  perpetual  decomposition  and  recomposition 
to  take  place,  which  is  not  improbable.  Another  fertile  source 
from  which  heat  is  derived,  is  the  physical  change  of  condition 
which  bodies  are  constantly  undergoing  in  nature,  as  for  example, 
the  conversion  of  gases  into  liquids,  of  liquids  into  solids,  &;c. 
by  taking  advantage  of  which  conversions  we  can  accumulate 
heat  at  will,  as  for  instance  by  the  condensation  of  steam.  When 
these  physical  changes  however  are  associated  with  chemical 
changes,  as  is  very  often  the  case,  the  most  striking  effects  are 
produced.     Of  this  kind  are  all  the  phenomena  of  combustion, 

pulsive  powers,  (as  in  the  radiation  of  light,  &c.)  the  cohesive  axes  of 
the  molecules  will  always  be  in  the  line  of  motion,  and  each  successive 
molecule  will  present  alternately  an  opposite  polarity  ;  while  the  chemi- 
cal axes  of  course  will  be  all  in  the  same  plane,  and  transverse  to  the  line 
of  motion.  Such  will  be  the  order  in  a  single  series  of  molecules  in  mo- 
tion ;  but  when  a  number  of  series  move  onward  together,  as  in  homo- 
geneous light,  there  is  reason  to  conclude  that  the  molecules  of  conti- 
guous series  have  a  tendency  to  arrange  themselves  thus  •.•.•.•••  with  the 
chemical  axes  at  right  angles  to  each  other.  Those  who  are  interested 
in  these  subjects  will  perhaps  readily  conceive  how  such  arrangements 
may  be  applied  to  explain  the  various  phenomena  we  have  been  consi, 
dering. 


G6  CHEMISTRY. 

the  most  common  source  of  artificial  heat ;  and  which  consists  of 
nothing  more  than  the  rapid  chemical  union  of  certain  bodies 
with  others,  and  generally  with  the  principle  termed  oxygen. 
Nearly  allied  to  chemical  action,  and  perhaps  identical  with  it, 
is  the  extrication  of  heat  by  organic  changes,  or  what  is  termed 
animal  heat ;  a  subject  we  shall  have  to  consider  in  a  future  part 
of  this  volume. 


We  have  thus  endeavoured  to  give  a  summary  view  of  the 
phenomena,  and  laws  of  motion  of  heat,  and  of  light.  In  conclu- 
sion it  only  remains  to  observe  that  these  phenomena  and  laws 
are  all  of  the  utmost  importance  in  the  economy  of  nature,  as 
constituting  limitations  and  principles  of  action,  to  which  the 
Great  Author  of  nature  most  rigidly  adheres  in  his  operations. 
Hence,  whether  we  view  the  distribution  of  heat  and  of  light  on 
the  large  scale,  as  regulating  climate ;  or  whether  we  view  them 
with  reference  to  the  most  trifling  particular,  as  the  clothing  of  a 
bud  or  of  an  insect;  we  find  the  same  beautiful  adaptation  and  con- 
trivance, everywhere  exemplified,  to  ensure  or  to  evade  the 
agency  of  these  all-important  principles.  The  wonderful  ar- 
rangements connected  with  heat  and  light  will  however  fall  more 
naturally  to  be  considered'  hereafter ;  we  shall  therefore  defer 
what  we  have  to  say  on  these  subjects  till  we  come  to  speak  of 
meteorology. 


Section  IX. 

Recapitulation  and  General  Observations  on  the  Subjects  treated 

of  in  the  preceding  Chapters. 

In  the  preceding  observations  we  have  endeavoured  to  give  a 
connected  sketch  of  the  nature  and  operation  of  molecular  forces  ; 
and  perhaps  it  will  still  further  facilitate  the  understanding  of  the 
subject,  if  we  recapitulate  briefly  the  leading  facts,  so  as  to  point 
out  to  those  who  may  not  be  inclined  to  peruse  the  foregoing  de- 
tails, the  analogy  that  prevails  throughout  the  whole. 

1.  In  the  first  place  we  attempted  to  show  that  the  forces 
which  determine  molecular  union  can  scarcely  be  those  of  mere 
gravitation,  in  their  ordinary  forms  at  least;  but  that  some  other 
modification  of  force  is  necessary  to  account  for  the  phenomena. 


RECAPITULATION.  67 

2.  By  assuming  the  molecules  of  bodies  to  be  virtually  sphe- 
roidal, and  endowed  with  two  kinds  of  polarizing  forces,  the  one 
operating  axially,  and  the  other  equutoriulhj,  we  attempted  to 
show  how  the  phenomena  of  simple  crystaUization  might  be  ex- 
plained ;  and  we  corroborated  our  argument  by  demonstrating 
that  the  electric  and  magnetic  forces  are  actually  related  to  each 
other,  precisely  as  we  assumed  the  energies  of  our  molecules  to 
be.  Hence  we  ventured  to  draw  the  conclusion,  that  electricity 
and  magnetism,  if  not  identical  with,  at  least  represent,  or  are 
analogous  to  those  forces,  the  existence  of  which  among  ponde- 
rable bodies  we  assumed  as  necessary  to  account  for  the  pheno- 
mena of  crystallization.  Further  we  attempted  to  render  it  pro- 
bable, that  the  molecules  of  the  imponderable  principles,  heat  and 
light,  possess  polarities  precisely  analogous  to  those  of  pondera- 
ble bodies,  and  that  many  of  their  peculiar  phenomena  depend 
upon  these  polarities. 

3.  In  attempting  to  account  for  the  different  forms  assumed  by 
bodies,  we- supposed  that  in  the  solid  form,  the  molecules  are  so 
arranged  as  to  attract  each  other  according  to  certain  laws ;  that 
in  the  liquid  form,  they  are  so  arranged  as  neither  to  attract  nor 
repel  each  other;  and  that  in  the  gaseous  form,  the  arrangement 
of  the  energies  of  the  molecules  is  such  as  to  render  them  mutu- 
ally repulsive.  Further,  by  assuming  that  those  molecules  which 
possess  the  property  of  attracting  each  other  in  the  solid  form  in 
preference  to  others,  retain  a  similar  relation  in  the  gaseous  form, 
and  repel  each  other  in  preference  to  others,  we  attempted  to  ac- 
count for  many  of  the  well  known  phenomena  of  gaseous  bodies. 

4.  Lastly,  we  attempted  to  show  that  the  phenomena  of  radia' 
tion  among  the  molecules  of  imponderable  bodies,  are  precisely 
analogous  to  the  phenomena  of  diffusion  and  mixture  among  the 
molecules  of  ponderable  bodies  when  in  the  liquid  and  gaseous 
states  ;  and  that  consequently  the  same  laws  are  strictly  applica- 
ble to  both. 

With  respect  to  the  reasons  which  have  induced  us  thus  to 
enter  into  the  dry  details  of  molecular  action,  and  which  may 
seem  to  require  some  apology  to  our  readers,  they  are  chiefly 
two-fold :  In  the  first  place,  as  connected  with  the  particular 
business  of  the  present  tieatise,  it  has  been  our  object  to  convey 
to  the  general  reader  some  idea  of  the  wonderful  operations  which 
are  constantly  taking  place  in  every  particle  of  matter  which  he 
sees  around  him,  or  to  use  the  language  of  Paley,  some  notion  of 
the  "  concealed  and  internal  operations  of  the  machine."  These 
operations  may  not  be  as  we  have  represented  them  ;  they  may 
in  fact  be  altogether  different ;  but  be  this  as  it  will,  a  perusal 
however  cursory,  of  what  has  been  stated,  can  hardly  fail  to  ac- 


68  CHEMISTRY. 

complish  one  purpose  we  had  in  view,  viz:  to  show  to  the  most 
incurious  and  superficial  reader  that  in  the  minutest  fragment  of 
matter,  and  in  the  commonest  and  simplest  operations  w^hich  take 
place  in  nature,  and  which  he  is  altogether  too  apt  to  overlook, 
the  most  wonderful  and  extraordinary  arrangements,  must  take 
place;  arrangements  which,  if  duly  considered,  are  calculated 
fully  as  much,  if  not  more,  than  those  connected  with  the  more 
striking  and  obvious  phenomena,  to  excite  his  wonder,  and  at 
the  same  time  to  display  the  wisdom  and  power  of  the  great 
Creator.  Tiie  second  object  we  aimed  at,  was,  as  just  stated,  to 
give  a  connected  and  popular  sketch  of  molecular  forces  and  ope- 
rations ;  and  by  placing  them  in  a  point  of  view  in  which  we 
believe  they  have  not  hitherto  been  considered,  to  display  the 
beautiful  simplicity  and  analogy  that  prevail  throughout  the 
whole. 

Finally,  it  remains,  before  we  close,  to  state  briefly  the  argu- 
ments deducible  from  the  divisibility  and  molecular  constitution 
of  matter,  with  reference  to  our  present  subject.  These  arguments 
may  be  considered  under  the  three  following  heads ;  first,  that 
matter  has  not  always  existed  in  its  present  form  ;  secondly,  it 
could  not  have  existed  in  its  present  form  by  chance  ;  and  thirdly, 
and  consequently,  that  it  must  have  been  the  work  of  a  voluntary 
and  intelligent  Being.  Other  deductions  might  doubtless  be  made 
from  what  has  been  stated,  but  these  we  purposely  avoid,  and 
confine  our  arguments  as  much  as  possible  to  grounds  admitting 
of  no  controversy. 

In  the  first  place,  the  divisibility  and  molecular  constitution  of 
matter  seem  to  prove  beyond  a  doubt  that  it  cannot  have  eternally 
existed  in  its  present  state. 

Although  we  can  form  no  idea  of  what  matter  would  be  with- 
out its  molecular  properties,  there  is  yet  nothing  in  these  properties 
which  can  induce  us  to  believe  that  tliey  are  necessary  to  the  mere 
existence  of  matter.  On  the  contrary,  we  have  seen  that  matter 
possesses  qualities  (those  of  gravitation)  of  a  more  primordial  kind, 
to  which  its  molecular  properties  are  apparently  secondary  or  sub- 
ordinate. But  if  these  subordinate  properties  be  not  necessary  to 
the  existence  of  matter,  matter  m\g\\i  possibly  at  some  time  have 
existed  without  them.  Now  this  very  possibility  is  incompatible 
with  eternal  existence;  for  eternal  (passive)  existence  necessarily 
involves  incapability  of  change.  Hence  the  molecular  constitution 
of  matter,  even  in  this  point  of  view,  must  be  supposed  to  have 
had  a  beginning;  and  when  we  consider  the  leading  and  charac- 
teristic property  of  matter  in  the  molecular  state,  viz.  the  endless 
repetition  of  exactly  similar  parts,  the  difiiculty  of  arriving  at 


GENERAL  ARGUMENTS.  69 

any  other  conclusion  is  exceedino;ly  increased.  It  is  to  be  observed 
also  that  the  above  remarks  apply  to  the  supposition  of  only  one 
form  of  matter  ;  but  we  shall  see  hereafter  that  chemists  recognize 
upwards  o^ fifty  forms  of  matter,  all  of  an  elementary  character ; 
at  least  we  cannot  at  present  say  that  one  of  these  forms  is  more 
elementary  than  another.  Again,  the  number  of  molecules  in  each 
of  these  elementary  principles,  great  as  it  is,  is  limited  ;  the  pro- 
perties of  the  molecules  also  are  fixed  and  definite,  all  which  cir- 
cumstances throw  further  insurmountable  difficulties  in  the  way 
of  the  supposition,  that  the  whole  have  existed,  as  they  now  ex- 
ist, from  eternity.  For  how  has  it  happeued,  it  may  be  asked, 
that  the  number  and  properties  of  the  elements,  and  the  molecules 
of  which  they  consist,  are  just  what  the  economy  of  nature  re- 
quires, and  neither  greater,  nor  less,  nor  different  ?  How  has  it 
happened,  that  what  is  supposed  to  be  infinite  in  some  respects, 
should  be  finite  and  limited  in  those  respects  in  which  we  are 
actually  able  to  trace  them  ;  and  what  is  more,  most  luckily  finite 
and  limited  just  M'here  they  appear  to  be  required  to  be  so?  He 
who  can  satisfactorily  answer  these  questions  may  contend  with 
some  prospect  of  success  for  the  eternity  of  matter  and  its  pro- 
perties ill  their  present  form.  In  the  mean  time  we  assert  with- 
out fear  of  contradiction,  that  the  molecular  constitution  of  matter 
is  decidedly  artificial ;  or  to  use  the  words  of  a  celebrated  writer, 
that  the  molecules  of  matter  have  all  "  the  essential  characters  of 
a  manufactured  article,"*  and  consequently  are  not  eternal. 

Secondly,  if  the  present  molecular  constitution  of  matter  has 
not  always  existed,  it  must  have  been  produced  at  some  time»  by 
some  cause  superior  to  itself.  Now  this  cause  must  have  ope- 
rated either  accidentally  and  by  chance  ;  or  voluntarily  and  under 
the  influence  of  a  ivill. 

With  respect  to  the  first  of  these  alternatives,  viz.  chance  ;  the 
endless  repetition  of  similar  parts  presented  by  the  molecular 
constitution  of  matter  seems  absolutely  to  preclude  this  supposition. 
Do  we  not  consider  it  a  subject  of  wonder  to  see  even  two  or 
three  things  by  chance  alike,  as  for  example  two  or  three  human 
faces?  Should  we  not  consider  the  man  absolutely  mad,  who 
would  attribute  the  uniform  and  manosuvres  of  a  regiment  of  sol- 
diers to  chance  ?  and  can  we  then  resist  the  argument  in  the  in- 
finitely stronger  shape  in  which  it  is  here  presented  to  us  !  Thus, 
as  the  idea  of  chance  seems  too  monstrous  to  be  entertained  for 
a  moment  by  any  rational  being  we  are  driven  irresistibly  to  the 
other  conclusion,  viz.  that  the  cause  or  agent  who  formed  the 
molecular  constitution  of  matter  was  a  voluntary  agent  or  Being  ; 

*  Sir  J.  Herschel  on  the  Study  of  Natural  Philosophy,  p.  38. 


70  CHEMISTRY, 

and  moreover  that  this  Being  possessed  a  power  commensurate 
with  his  will. 

Thirdly ;  tlie  agent  or  Being  who  constructed  the  wonderful 
system  we  have  been  considering  must  have  been  as  intelligent 
as  he  was  powerful. 

We  infer  intelligence  in  an  agent  from  the  fitness  and  adapta- 
tion to  certain  ends  exemplified  in  his  works.  Thus,  when  we 
see  a  machine  admirably  fitted  for  the  office  it  perfi)rms,  we  infer 
that  the  maker  of  that  machine  must  have  possessed  intelligence. 
Now  if  we  judge  of  the  molecular  constitution  of  matter  by  this 
rule,  we  shall  find  that  there  is  not  only  the  most  extraordinary 
fitness  and  adaptation  to  circumstances  displayed  in  its  arrange- 
ments, as  far  as  we  can  understand  them,  but  evidently  much 
further ;  that  is  to  say,  the  maker  of  this  system  must  not  only 
have  possessed  intelligence,  but  intelligence  infinitely  surpassing 
our  own.  Thus  at  the  very  beginning,  the  selection  of  the 
molecular  form  of  matter  out  of  the  many  possible  forms  which 
might  be  supposed  to  exist,  may  be  considered  as  an  instance  of 
intelligence  of  the  highest  kind ;  for  this  alone,  of  all  the  forms 
that  can  be  conceived,  seems  best  adapted  to  the  purposes  of 
creation.  Indeed,  on  what  other  supposition,  than  that  of  the 
subdivision  of  matter  into  minute  similar  pcn'ts,  could  all  those 
endless  operations  which  we  see  constantly  going  on  in  the  world, 
be  imagined  to  take  place  ?  Moreover,  the  nature  of  the  powers 
with  which  the  molecules  of  matter  are  endowed  is  truly  asto- 
nishing, and  calculated  in  the  highest  degree  to  impress  us  with 
exalted  notions  of  the  intelligence  and  power  of  their  conti-iver. 
Thus,  what  can  be  more  wonderful,  than  that  the  self-same 
chemical  forces  differently  directed  should  produce,  not  only  all 
that  endless  change  of  property,  of  form,  and  of  condition  wdiich 
we  see  around  us,  and  which  are  so  beneficial  and  even  necessary 
to  our  existence  ;  but  likewise  some  of  the  most  terrible  displays 
of  power  in  nature  ;  as  for  instance,  the  utmost  intensities  of  heat, 
of  cold,  and  of  light;  the  terrors  of  the  thunderbolt,  and  the  irre- 
sistible energies  of  the  earthquake  !  Nor  on  the  other  hand,  are 
the  cohesive  aflinities  existing  among  the  molecules  of  matter 
much  less  wonderful  or  important ;  for  if  similar  molecules  had 
not  been  constituted  with  self-attractive  and  self-repulsive  powers, 
there  would  have  been  no  aggregation  of  the  same  matter  into 
symmetrical  groups,  no  order  or  regularity,  no  separation  or  pu- 
rity ;  in  short  there  would  have  been  no  common  bond  of  union, 
and  the  whole  would  have  been  dispersed  throughout  nature,  as 
accident  or  other  circumstances  might  determine.  Hence  the 
present  order  of  things  could  not  have  existed  unless  the  mole- 
cules of  matter  had  been  endowed  with  both  these  properties  ; 


ELEMENTARY  PRINCIPLES.  71 

one  of  which  the  chemical^  as  it  were,  goes  before  and  imperi- 
ously determines  what  molecules  shall  be  combined  or  separated; 
while  the  other,  the  cohesive,  silent  and  unobtrusive,  follows  in 
its  train,  and  industriously  assorting  and  arranging  its  predeces- 
sors' labours,  here  perhaps  forms  a  diamond,  or  there  superin- 
tends the  integrity  of  the  atmosphere  ! 

Such  are  molecular  forces  as  they  obviously  appear  to  us,  and 
such  the  arguments  deducible  from  them.  But  when  w^e  attempt 
to  go  further,  and  inquire  into  the  intimate  nature  of  these  forces, 
we  not  only  find  much  that  is  unknown  to  us,  but  much  that  ap- 
parently surpasses  our  utmost  conception  !  And  what  a  still 
more  sublime  idea  is  this  calculated  to  convey  to  us  of  the  wisdom 
and  power  of  tliat  Being  who  contrived  and  made  tiie  whole  ! 
When  and  where,  do  we  naturally  exclaim,  did  this  Being  exist? 
whence  his  wisdom,  and  whence  his  power?  There  is,  there 
can  be,  but  one  answer  to  these  inquiries.  The  Being  who  con- 
trived and  made  all  these  things  must  have  pre-existed  from 
eternity — must  have  been  omniscient — must  have  been  omnipo- 
tent  MUST  HAVE  BEEN  GoD  ! 


CHAPTER  IV. 

OF  CHEMICAL  ELEMENTARY  PRINCIPLES,  AND  OF  THE  LAWS  OF  THEIR 

COMBINATION. 

In  the  preceding  chapter  we  have  endeavoured  to  show  that 
the  minutest  fragment  of  homogeneous  matter  cognizable  by  our 
senses  is  composed  of  innumerable  molecules,  all  of  which  are 
exactly  alike  in  size,  in  shape,  in  properties,  in  short,  of  every 
kind ;  and  we  argued  that  these  facts  incontestibly  prove  that 
these  molecules  could  not  always  have  existed  in  their  present 
form,  nor  have  been  formed  by  chance,  but  that  they  must  have 
had  a  beginning,  and  have  been  the  work  of  a  Creator.  Now 
when  we  consider  the  prodigious  quantity  of  matter  composing 
our  globe  (to  go  no  further)  or  even  composing  a  portion  of  it, 
as  for  example,  the  mass  of  water  existing  in  the  ocean,  and  re- 
flect that  every  individual  molecule  of  this  water  possesses  pro- 
perties exactly  like  those  of  the  drop  we  formerly  contemplated, 
our  argument,  already  sufliciendy  convincing,  actually  over- 
whelms us  with  its  force.  Still  however  it  admits  of  further 
corroboration ;  and  we  proceed  now  to  show  that  all  this  vast  as- 
semblage of  molecules,  so  numerous,  so  diversified,  so  extraordi- 
nary as   they  are,  may  be  reduced  to  a  very  {qwv   elementary 


72  CHEMISTRY. 

groups,  upon  the  endless  combinations  and  separations  of  which 
all  the  phenomena  of  chemistry  depend. 


Section  I. 
Of  Chemical  Elementary  Principles. 

The  substances  at  present  considered  as  elementary  amount  to 
about  fifty-four.  Of  these  several  possess  certain  properties  in 
common,  though  they  all  differ  from  one  another  in  subordinate 
particulars,  or  in  other  words,  are  specifically  different.  Of  the 
whole  number  not  above  two  or  three  exist  in  any  great  quantity 
in  an  uncombined  state,  at  least  in  those  parts  of  our  globe  to 
which  we  have  access,  but  the  whole  are  wrapped  up  as  it  were 
and  have  their  properties  concealed  in  compounds.  Under  ordi- 
nary circumstances  most  elementary  principles  exist  as  solids,  but 
some  of  the  more  important  occur  in  a  gaseous  form,  and  one  or 
two  as  fluids.  A  few  of  them  are  apparently  of  so  little  conse- 
quence in  the  world,  that  if  they  were  annihilated  they  would 
scarcely  be  missed;  while  others  of  them,  on  the  other  hand,  are 
so  obviously  necessary  to  the  existence  of  the  present  order  of 
things,  that  the  least  derangement  or  alteration  in  their  proportion 
or  quantity  would  be  fatal  to  the  whole.  Some  of  these  element- 
ary substances  exist  in  such  enormous  quantities  as  to  constitute  a 
large  proportion  of  the  whole  visible  bulk  of  our  globe,  while  others 
again,  occur  in  such  minute  proportion,  at  least  within  our  reach, 
as  to  be  obtained  with  difficulty  and  not  without  elaborate  research. 
With  respect  to  the  facility  with  which  they  enter  into  combina- 
tion, and  the  obstinacy  with  which  they  unite,  they  differ  also 
very  remarkably ;  a  few  of  them  combining  readily  in  a  variety 
of  proportions  with  almost  all  the  rest,  while  some  of  the  others 
can  be  scarcely  made  to  combine  under  any  circumstances.  Lastly, 
with  respect  to  the  influences  which  different  elementary  sub- 
stances are  capable  of  exerting  upon  organic  life,  these  are  equally 
striking.  A  large  majority  of  them  indeed  may  in  their  simple 
state,  be  considered  of  a  deleterious  nature  :  while  three  or  four 
of  them,  on  the  other  hand,  make  organized  beings  what  they  are, 
and  are  necessary  to  their  very  existence. 

Such  are  a  few  of  the  leading  properties  of  the  elementary  prin- 
ciples as  we  are  at  present  acquainted  willi  tliem  ;  in  the  following 
table  from  Dr.  Thomson  they  are  arranged,  as  far  perhaps  as  is 
practicable,  according  to  their  chemical  characters. 


ELEMENTARY  PRINCIPLES. 


73 


TABLE. 


1  Oxygen. 

2  Chlorine. 

3  Bromine. 

4  Iodine. 

5  Fluorine. 


6 
7 
8 
9 
10 


Hydrogen. 
Carbon. 
Azote. 
Boron. 
Silicon. 


11  Phosphorus. 

12  Sulphur. 

13  Selenium. 


14  Arsenic. 

15  Antimony. 

16  Tellurium. 

17  Chromium. 

18  Uranium. 

19  Vanadium. 

20  Molybdaenum. 

21  Tungsten. 

22  Titanium. 

23  Columbium. 


24  Potassium. 

25  Sodium. 

26  Litliium. 


27  Calcium. 

28  Magnesium. 

29  Strontium. 

30  Baryum. 

31  Aluminum. 

32  Clucinum. 

33  Yttrium. 

34  Zirconium. 
25  Thorinum. 

36  Iron. 

37  Manganese. 

38  Nickel. 

39  Cobalt. 

40  Cerium. 


41  Zinc. 

42  Cadmium. 

43  Lead. 

44  Tin. 

45  Bismuth. 

46  Copper. 

47  Mercury. 

48  Silver. 

49  Gold. 

50  Platinum. 

51  Palladium. 

52  Rhodium. 

53  Iridium. 

54  Osmium. 


It  is  foreign  to  the  object  of  this  work  to  enter  into  a  minute 
description  of  these  bodies  ;  we  shall  therefore  content  ourselves 
with  such  a  view  of  them  as  may  enable  the  general  reader 
to  form  some  idea  of  their  properties,  and  to  follow  us  without 
much  difficulty  in  our  subsequent  remarks. 

The  five  first  bodies,  Oxygen,  Chlorine,  Bromine,  Iodine,  and 
Fluorine,  are  usually  termed  supporters  of  combustion.  They 
have  some  properties  in  common,  though  in  other  respects,  and 
particularly  in  their  apparent  relative  importance  in  the  economy 
of  nature  they  differ  exceedingly.  Tbey  are  remarkable  for  the 
tendency  they  have,  not  only  to  combine  with  one  another,  but 
with  almost  all  the  bodies  below  them  in  the  table ;  and  their  union, 
particularly  that  of  oxygen,  is  usually  accompanied  with  the  ex- 
trication of  more  or  less  of  heat  and  light,  and  constitutes  the  well- 
known  phenomena  termed  combustion. 

(1)  Oxygen  is  one  of  the  very  few  elementary  substances  that 
occur  naturally  in  the  gaseous  form,  in  which  form  it  constitutes 
about  one  fifth  part  of  common  air.  As  the  world  at  present  ex- 
ists,   oxygen,    perhaps,   may  be    fairly  considered    as  one  of  the 

1.  Oxygen,  from  o^vc,  acid,  and  yivvdco,  to  generate  ;  from  its  property 
of  forming  acids.  2.  Ciilorine,  from  x^u^c;,  green  ;  so  called  from  its 
colour.  3  Bromine,  from  0^Z/uoc,  fetid;  so  called  from  its  strong  odour. 
4.  Iodine,  from  ^JqhS}];  violet  ;  from  the  colour  it  assumes  in  the  gaseous 
state.  6.  Hydrogen,  from  vSce^,  water,  and  yivvdai,  to  generate.  8.  Azote, 
from  a  privative  and  ^an),  life  ;  from  its  bein^  incapable  of  supporting  life. 
13.  Selenium,  from  ^ihhvn,  the  moon.  17.  Chromium,  from  ;;^^J:^ot  colour  ; 
so  called  from  the  beautiful  colours  of  some  of  its  salts.  18.  Uranium, 
from  ciu^tfvo?,  the  heavens.  19.  Vanadium,  from  vanadis,  a  Scandinavian 
deity.  20.  Molybdaenum,  from  Mo\v^Su.iv<t.,  lead.  22. Titanium,  from  T/ravof, 
calx.  23.  Columbium,  from  Columbia,  in  America,  where  it  was  first 
found.  26.  Lithium,  from  A/6oc,  a  stone.  29.  Strontium,  from  Strontian, 
the  name  of  a  place  in  Scotland,  where  first  found.     50.  Baryum,  from 


74  CHEMISTRY. 

most  important,  if  not  the  most  important  substance  in  it.  From 
its  proneness  to  enter  into  composition  it  is  constantly  operating 
upon,  and  modifying  everything.  By  far  the  greater  proportion 
of  mineral  bodies  forming  the  crust  of  the  earth,  contain  more  or 
less  of  it;  and  in  all  plants  and  animals  it  actually  exists  as  a  con- 
stituent elementary  principle.  In  short,  the  properties  of  oxygen 
stamp  it  as  an  element  and  subordinate  agent  of  the  most  important 
kind;  while  the  numberless  contrivances  which  are  observable  in 
nature,  to  secure,  or  evade,  or  modify  its  operations,  are  most  ex- 
traordinary, and  exhibit  some  of  the  m.ost  marked  and  unequivocal 
evidences  of  design  on  the  part  of  their  great  Contriver,  that  we 
meet  with  among  his  works.  Several  of  the  most  important  of 
these  contrivances  we  shall  have  occasion  to  allude  to  hereafter  ; 
but  there  is  one  of  so  curious  and  interesting  a  character  that  it 
may  be  mcrrtioned  here  as  an  illustration  of  the  above  remarks. 
The  nature  and  mechanism  of  the  function  of  respiration  will  be 
explained  elsewhere,  and  it  is  sufficient  for  our  present  purpose 
to  state  that,  by  means  of  a  complicated  apparatus,  the  blood  is 
made  to  circulate  through  the  lungs,  in  order  that  it  may  be  there 
exposed  to  the  oxygen  of  the  atmosphere.  For  purposes  beyond 
our  comprehension,  but  probably  in  part  at  least  with  a  view  to 
the  future  creation  of  organized  beings,  the  great  Architect  of  the 
universe  had  willed  that  this  principle  should  exist  upon  the  sur- 
face of  our  globe  in  a  gaseous  state ;  when  he  created  animals  he 
chose  also  to  render  them  dependent  upon  oxygen  for  their  ex- 
istence ;  and  he  effects  his  object,  not  by  bending  this  principle 
to  his  purpose,  by  altering  its  physical  or  other  properties  ;  not 
by  obtaining  it  from  v/ater,  or  any  of  the  innumerable  compounds 
into  which  it  enters,  wiiich  according  to  our  imperfect  notions  he 
might  have  more  easily  done  ;  but,  as  if  on  purpose  to  display 
his  power  and  design,  he  rigidly  adheres  to  the  properties,  both 
mechanical  and  chemical,  imparted  to  oxygen,  and  to  these  pro- 
perties accommodates  his  future  labours  !  The  whole  therefore 
of  the  complicated  and  beautiful  apparatus,  connected  with  the 
respiration  of  animals,  is  most  obviously  designed  and  constructed 
with  reference  to  the  properties  of  the  oxygen  of  the  atmosphere, 
and  altogether  they  afford  one  of  the  most  striking  evidences  of 
adaptation  and  design  presented  to  us  in  nature. 

(2)   Chlorine  in  its  elementary  state  is   a  gas,   having  all  the 

Bstg  t^f,  heavy.  Aluminum,  from  Alumen,  alum.  32,  Glucinum,  from 
Ykvku;^  sweet  ;  from  the  taste  of  some  of  its  saUs.  52.  Rhodium,  from 
'PoSov,  a  rose  ;  from  the  colour  of  some  of  its  compounds.  53.  Iridium, 
from  ipii;  the  rainbow  ;  froin  the  variety  of  colours  assumed  by  some  of 
its  salts.  54.  Osmium,  from  'Oa-fA)),  odour  5  from  the  strong  smell  emitted 
by  some  of  its  compounds. 


CHLORINE.       BROMINE,       IODINE.       FLUORINE.  75 

mechanical  properties  of  common  air,  but  in  this  form  it  never 
occurs  naturally.  It  exists  however  in  great  abundance  in  a  state 
of  combination,  from  which  it  may  be  readily  obtained  by  easy 
chemical  processes.  One  of  the  most  abundant  sources  of  chlo- 
rine is  common  salt,  into  which  it  enters  in  the  proportion  of 
about  60  per  cent.  As  compared  with  oxygen  chlorine  is  much 
less  abundant  and  perhaps  important;  yet  it  is  doubtful  if  with- 
out chlorine  the  present  order  of  things  could  proceed.  Take 
for  example  the  familiar  instance  of  common  salt  above  referred 
to.  Let  us  consider  the  universal  diffusion  of  this  substance 
throughout  nature — what  the  sea  would  be,  or  how  animals 
could  exist,  without  it— let  us  consider  these  and  the  numberless 
other  operations  which  this  valuable  compound  more  or  less 
enters  into,  or  influences,  and  we  shall  be  able  to  form  some 
notion  of  the  part  chlorine  bears  in  the  economy  of  nature.  On 
the  other  hand,  when  we  reflect  that  were  chlorine  to  be  extri- 
cated from  its  state  of  combination,  and  made  to  exist,  like  oxy- 
gen, in  a  gaseous  form,  that  it  would  instantly  prove  fatal  to 
organized  beings  ;  can  we  fail  to  be  struck  with  the  very  obvious 
design  thus  displayed  in  rendering  its  quantity  and  combining 
powers  such  as  to  keep  it  in  a  state  of  union,  and  by  these  means 
to  secure  all  its  useful  without  its  deleterious  properties? 

(3)  (4)  Bromine  and  Iodine,  the  next  two  substances,  are 
found  principally  in  sea-water  and  in  marine  productions.  They 
appear  to  exist  in  very  minute  proportion,  and  always  in  a  state 
of  combination.  Bro7nine  exists  under  ordinary  circumstances 
as  a  deep-coloured  red  fluid,  having  a  very  strong  and  offensive 
odour  ;  Iodine  is  a  crystallized  solid,  volatile  by  a  slight  increase 
of  temperature,  and  forming  a  beautiful  violet  vapour.  Bromine 
and  Iodine  more  nearly  resemble  chlorine  than  oxygen  in  their 
properties,  though  they  differ  materially  from  both,  and  their  use 
in  the  economy  of  nature  is  absolutely  unknown.  It  may  how- 
ever be  observed  that  Iodine  has  lately  been  much  celebrated  for 
its  medicinal  properties."*^ 

(5)  Fluorine  has  been  rather  inferred  than  demonstrated  to 
exist.     It  occurs  principally  in  the  mineral  called  Fluor  spar,  in 


*  It  may  not  be  amiss  to  observe  here  that  the  author  of  the  present 
volume  first  employed  the  hydriodate  of  potash,  as  a  reinedy  for  g-oitre, 
in  the  year  1816,  after  having"  previously  ascertained,  by  experiments 
upon  himself,  that  it  was  not  poisonous  in  small  doses  as  had  been  repre- 
sented. Some  time  before  the  period  stated,  this  substance  had  been  found 
in  certain  marine  productions  ;  and  it  struck  the  author  that  burnt  sponge 
(a  well  knov/n  remedy  for  g-oitre)  might  owe  its  properties  to  the  pre- 
sence of  Iodine,  and  this  was  his  motive  for  making-  the  trial.  He  lost 
sig-ht  of  the  case  in  which  the  remedy  was  employed,  before  any  visible 


76  CHEMISTRY. 

a  state  of  combination  with  lime,  and  in  this  state  it  would  seem 
lo  be  harmless;  but  in  a  state  of  purity  it  is  exceedingly  delete- 
rious. One  of  its  most  remarkable  properties  is  that  of  corroding 
glass. 

We  pass  on  now  to  a  very  different  class  of  substances,  and 
which  instead  of  having  the  power  of  supporting  combustion  in 
other  substances,  are  for  the  most  part  themselves  combustible.  Of 
these,  the  first  and  perhaps  the  most  important  we  have  to  no- 
tice is 

(6)  Hydrogen.  This  principle  in  its  elementary  state  exists 
as  a  gas,  having  all  the  mechanical  properties  of  common  air.  In 
this  state  it  is  exceedingly  inflammable;  and  if  mixed  v.'ith  oxy- 
gen, and  if  the  mixture  be  exposed  to  heat,  the  two  gases  unite 
suddenly  and  violently  with  a  loud  explosion  ;  while  the  result 
of  the  combustion  is  water.  Hydrogen  is  the  lightest  body 
known,  and  under  the  same  bulk  therefore  contains  less  matter 
than  any  otlier  body.  It  does  not  exist  naturally  in  a  separate 
state,  but  always  in  combination  ;  and  by  far  most  generally  and 
abundantly  in  combination  with  oxygen  in  the  form  of  water. 
Hydrogen  ranks  perhaps  next  to  oxygen  in  importance  ;  at  least 
as  far  as  organized  beings  are  concerned  ;  since  like  oxygen  it 
constitutes  one  of  the  elementary  principles  of  which  they  are 
formed.  It  differs  however  remarkably  from  oxygen,  in  not 
being  in  its  elementary  state  necessary  to  the  existence  of  or- 
ganized beings  ;  indeed  hydrogen  is  actually  incompatible  with 
the  existence  of  animals,  if  not  of  vegetables  ;  and  its  properties 
as  an  element  have  evidently  been  sacrificed  to  its  properties  as 
a  compound,  that  is  to  say,  to  its  properties  as  ivater.  Hence 
we  have  to  admire  tlie  happy  adjustment  of  the  quantities  of  the 
two  elements  to  each  other,  so  that  the  oxygen  shall  predominate ; 
an  adjustment  that  can  scarcely  be  explained  upon  any  other 
supposition  than  that  of  design  ;  for  any  other  cause,  as  chance, 
would  have  been  quite  as  likely  to  have  produced  an  excess  of 
hydrogen  as  of  oxygen,  or  at  least  anything  but  the  exact  pro- 
j)ortions  required.  Lastly,  it  may  be  remarked,  that  to  the  rela- 
tive proportions  of  oxygen  and  hydrogen  existing  on  our  globe, 
more  than  perhaps  to  any  other  subordinate  cause,  the  present 
order  of  things  owes  its  stability.  For  the  proportions  of  these 
principles  are  so  happily  adjusted  and  balanced,  and  all  the  nu- 
merous operations  dependent  upon  them  are,  in  consequence,  so 

alteration  was  made  in  the  state  of  the  disease  ;  but  not  before  some 
of  the  most  strikinjij  cfTccts  of  the  remedy  were  observed.  The  above 
employment  of  the  compounds  of  Iodine  in  medicine  was  at  the  time 
made  no  secret;  and  so  early  as  1819,  the  remedy  was  adopted  in  St. 
Thomas's  Hospital,  by  Dr.  Elliotson,  at  the  author's' sug-g-estion. 


CARBON.  77 

firmly  establislied,  that  no  material  change  can  possibly  happen 
to  any  part  from  an  internal  cause,  but  if  changed  at  all,  the  whole 
must  be  changed  from  without. 

(7)  Carbon,  or  charcoal,  is  a  substance  too  well  known  in  its 
ordinary  state  to  require  description  ;  in  its  crystallized  and  pure 
state  it  is  found  to  constitute  the  diamond,  the  hardest  and  most 
brilliant  body  in  nature  ;  a  circumstance  that  certainly  could  not 
have  been  anticipated,  but  which  affords  a  most  striking  instance 
of  the  effects  produced  by  the  different  modes  in  which  molecules 
of  the  same  matter  may  be  aggregated.     Carbon  perhaps  more 
than  any  other  principle  may  be   considered  as  constituting  the 
slaminal  or  fundamental  element  entering  into  the  composition  of 
organized  beings.     This  is  particularly  the   case  in  principles 
from  the  vegetable  kingdom,  which  owe  their  peculiar  character 
essentially  to  carbon,  and  their  endless  varieties  to  differences  in 
its  quantity,  and  to  the  modifying  influence  of  the  hydrogen  and 
oxygen  with  which  it  is  associated.     In  animal  substances,  car- 
bon exerts  a  similar  influence,  but  its  effects  are  materially  modi- 
-fied  by  the  presence  of  another  staminal  principle  to  be  presently 
considered.     Carbon,  in  some  state  or  other,  exists  in  considera- 
ble quantities  upon  the  surface  of  our  globe,  but  apparently  by  no 
means  in  so  large  a  proportion  as  oxygen  and  hydrogen.     Ex- 
clusively of  that  actually  involved  in  the  composition  of  organized 
beings,  carbon  is  met  with  nearly  pure  in  large  quantities  in  par- 
ticular districts  in  the  well-known  form  oi  fossil  coals;   but  it 
occurs  in  far  greater  proportion  in  combination  with  oxygen  in 
i\\e  iouTi  oi  carbonic  acid;  which  carbonic  acid  in  union  with 
lime,  constitutes  common  chalk  and  limestone,  two  of  the  most 
abundant  minerals  in  nature.*     Carbon  in  its  elementary  slate,  is 
a  very  inert  substance,  and  is  scarcely  liable  to  be  affected  by,  or 
to  affect   organized  beings  ;  but  with   hydrogen  and  oxygen  it 
forms  gaseous  compounds  of  great  activity,  and  capable  of  proving 
instantly  fatal  to  animals  respiring  them.    Such  effects,  however, 
appear  to  be  obviated  by  a  beautiful  expedient  which  we  shall 
have  occasion  more  particularly  to  notice  hereafter.    In  the  mean 
time  it  may  be  observed,  that  though  the  compound  of  carbon 
and  oxygen  {carbonic  acid)  is  by  innumerable  processes  con- 
stantly  forming    around  us   in   enormous    quantities  ;  by  some 
compensating  means  it  disappears  as  fast  as  it  is  formed ;  so  that 

*  In  order  to  give  some  idea  of  the  proportion  in  which  carbon  exists 
in  different  common  substances,  it  may  be  observed  that  a  pound  of  char- 
coal is  equal  to,  and  is  contained  in  rather  more  than,  two  pounds  of  su- 
gar or  flour,  and  eight  of  potatoes  or  limestone;  so  that  a  mountain  of 
limestone  contains  the  essential  element  of  at  least  an  equal  bulk  of 
potatoes,  and  of  a  forest  that  would  amply  cover  manv  such  mountains. 

7* 


78  CHE3IISTRY. 

the  atmosphere,  which  wuhout  this  provision  wouUl  probably 
before  now  have  become  contaminated  by  carbonic  acid  to  an  ex- 
tent fatal  to  animal  life,  barely  contains  traces  of  it. 

(8)  Azote  or  nitrogen  is  one  of  the  very  few  elementary  prin- 
ciples which  exist  naturally  in  an  uncombined  state.  It  constitutes 
about  4-5ths  or  80  per  cent,  of  common  air,  the  rest  being  princi- 
pally oxygen.  The  great  bulk  of  this  principle  in  existence  is 
confined  to  the  atmosphere,  and  to  animal  substances,  of  which 
it  forms  a  constituent  element ;  and  it  enters  very  little  into  natural 
mineral  productions.  In  its  pure  state,  azote  is  remarkable  for 
its  negative  properties,  that  is  to  say,  for  the  difficulty  with  which 
it  enters  into  combination  with  other  matters.  Thus  it  is  neither 
combustible  nor  a  supporter  of  combustion ;  is  neither  acid  nor 
alkaline  ;  possesses  neither  taste  nor  smell  ;  nor  does  it  directly 
combine  with  any  other  known  substance.  Yet  when  made  by  pe- 
culiar management  to  unite  with  oxygen,  hydrogen,  or  carbon,  azote 
forms  some  of  the  most  energetic  compounds  we  possess  :  thus, 
inixed  with  oxygen  it  forms  atmospheric  air,  as  before  observed  ; 
united  with  oxygen  it  forms  aquafortis,  tlie  most  corrosive  of 
liquids  ;  united  with  hydrogen  it  forms  the  volatile  alkali  or  am- 
monia, likewise  an  energetic  compound,  but  of  an  opposite  nature; 
while  united  with  carbon  and  hj'drogen,  it  ionns prussic  acid,  the 
most  virulent  poison  in  existence  !  Azote  may  be  considered  as 
constituting  the  characteristic  element  of  animal  substances,  and 
as  imparting  to  them  their  peculiar  properties  ;  in  this  j)oint  of 
view  therefore  it  is  a  principle  of  very  great  importance.  More- 
over, the  above  mentioned  negative  properties  of  azote  are  evi- 
dently of  a  primordial  kind,  and  seem  to  have  been  formed  with 
reference  to  future  creations,  which  have  all  been  most  carefully 
and  rigidly  adapted  to  them.  Thus  had  the  properties  of  azote 
not  been  negative,  those  of  its  most  important  compound,  atmo- 
spheric ai  r  could  not  have  been  negative  ;  and  atmospheric  air  might 
have  been  acid  or  alkaline,  or  have  possessed  odour  or  colour; 
either  of  which  circumstances  would  have  been  incompatible  with 
the  present  order  of  things. 

(9)  (10)  Boron  and  Silicon.  The  next  two  substances  obtain 
their  names  from  borax  and  silex,  the  natural  productions  in  which 
they  exist  in  a  state  of  combination.  Borax  is  a  saline  production 
chiefly  found  in  certain  lakes  in  Thibet  and  China.  Boron,  the 
elementary  substance  obtainable  from  it,  is  a  deep  brown  powder 
possessing  neither  taste  nor  smell,  but  highly  inflammable  at  a 
temperature  below  a  red  heat.  Silicon  is  the  elementary  basis  of 
silex  or  common  (lint,  one  of  the  most  abundant  minerals  in  nature. 
Silicon  is  a  brown  powder  very  similar  to  boron  in  appearance, 
and  like  it  inflammable  under  certain  circumstances.     'I'hese  two 


PHOSPHORUS.  79 

elementary  principles  do  not  exist  naturally,  but  have  been  formed 
by  elaborate  chemical  processes  in  small  quantities  only.  They 
seem  to  be  more  nearly  allied  to  carbon,  in  their  properties,  than 
to  any  other  elementary  product.  Borax  exists  in  very  small 
quantities,  and  its  use  in  the  economy  of  nature  is  not  apparent. 
Silex  on  the  other  hand  is  a  most  important  production,  and  in 
its  hardness,  insolubiUty,  and  other  refractory  properties,  we  re- 
cognize a  substance  admirably  adapted  for  the  purpose  to  which 
it  has  evidently  been  designed,  viz.  that  of  constituting  the  stamina 
or  ground-work,  as  it  M'ere,  of  our  globe,  and  which  could  not 
be  withdrawn  without  subverting  the  whole.  Silex  is  found  in 
small  quantities  both  in  plants  and  in  animals,  but  does  not,  like 
hydrogen,  oxygen,  carbon,  and  azote,  form  a  constituent  element 
of  organized  beings. 

(11)  Pliosphorus,  under  ordinary  circumstances,  is  a  pale  am- 
ber-coloured substance,  very  like  wax  in  appearance,  but  so  ex- 
ceedingly combustible  that  it  cannot  be  heated,  much  less  melted 
in  the  open  air,  without  immediately  taking  fire.  Under  these 
circumstances,  as  may  be  supposed,  it  does  not  exist  naturally, 
but  is  obtained  by  an  elaborate  process  from  various  compounds 
into  which  it  enters  ;  as  for  example,  from  hone  earth,  or  the 
earthy  basis  of  the  bones  of  animals  ;  and  also  from  certain  salts. 
It  exists  also  in  the  mineral  kingdom  in  certain  districts  in  con- 
siderable  quantities,  but  upon  the  whole,  it  is  not  an  abundant 
principle.  Phosphorus  affords  another  beautiful  instance  in  which 
the  design  has  been  directed  to  the  properties  of  the  compound, 
rather  than  to  the  element  itself.  The  phosphate  of  lime  or  bone 
earth  was  apparently  the  thing  wanted  to  constitute  the  bony 
skeleton  of  animals,  and  accordingly,  to  this  compound  the  pro- 
perties of  the  element  itself  seem  to  have  been  sacrificed.  Neither 
lime  itself  in  mass,  nor  any  of  its  mineral  compounds,  appear  to 
be  adapted  for  forming  a  constituent  principle  of  a  living  organized 
being.  It  was  necessary  therefore  to  have  a  connecting  medium, 
or  link,  that  should  unite  organization  with  the  mineral  constitu- 
ent, and  phosphorus  admirably  accomplishes  this  ol)ject.  Accord- 
ingly, we  see  that  organization  goes  on  in  conjunction  with  lime 
in  the  bones  of  animals,  through  the  medium  of  this  element,  quite 
as  readily  as  in  other  parts  of  their  system  ;  whereas  when  phos- 
phorus is  absent,  as  in  shells,  and  in  other  deposits  of  carbonp.te 
of  lime,  the  carbonate  of  lime  is  extravascular,  and  seems  to  form 
no  part  of  the  living  system.  There  are  also  other  important  of- 
fices which  this  principle  evidently  performs  in  the  animal  econo- 
my, some  of  which  we  shall  have  occasion  to  refer  to  hereafter. 

(12)   Sulphur.     This  well  known  substance  is  one  of  the  Aery 
few  that  exist  naturally  in  an  elementary  state.    It  is  a  very  abun- 


80  CHEMISTRY. 

dant  and  probably  important  principle  in  the  economy  of  nature, 
as  it  not  only  exists  in  large  quantities  in  the  mineral  kingdom, 
but  in  a  greater  or  less  proportion  in  almost  all  animal,  and  in 
many  vegetable  products.  Its  uses,  however,  at  present,  are  very 
imperfectly  understood.  Sulphur  combines  with  hydrogen,  and 
forms  a  very  deleterious  gaseous  compound.  Its  combinations 
with  oxygen  are  generally  acid,  and  very  active  in  their  concen- 
trated form,  but  not  poisonous. 

(13)  Selenium^  the  next  substance,  is  found  in  very  minute 
quantities  generally  associated  with  sulphur,  which  in  its  properties 
it  somewhat  resembles  ;  or  rather,  perhaps  it  appears  to  consti- 
tute the  connecting  link  between  sulphur  and  the  metals.  The  uses 
of  selenium  in  the  economy  of  nature  are  unknown  ,  but  we  shall 
have  occasion  hereafter  to  refer  to  its  compound  with  hydrogen, 
which  is  even  more  deleterious  than  the  compound  of  sulphur  with 
this  element. 

(14)  ^6lr.senic  in  its  pure  state  is  a  metalloid,  or  imperfectly 
metallic  substance,  having  much  the  appearance  of  polished  steel. 
In  the  form  in  which  it  is  popularly  known,  as  ichife  arsenic,  it 
is  combined  with  oxygen,  and  constitutes  one  of  the  most  virulent 
of  poisons.  Arsenic  exists  in  certain  minerals  in  considerable  quan- 
tities, and  seems  in  every  form,  to  be  incompatible  with  organic  life. 

(15)  Antimony  is  usually  found  in  nature  associated  with  sul- 
phur, the  compound  it  forms  with  which,  was  for  along  time  con- 
sidered as  the  metal  itself.  In  its  pure  state,  antimony  has  a  bluish- 
grey  colour,  and  possesses  considerable  metallic  splendour,  but 
in  this  form  it  seldom  occurs  in  nature.  The  compounds  of  anti- 
mony are  active  medicinal  agents,  and  some  of  them  are  much 
employed  for  that  purpose. 

(16)  (17)  (18)  (19)  (20)  (21)  (22)  (23)  TeUurium,  Chromium, 
Uraniiwi,  Vanadium,  Molybdsenum,  Tungsten ,  Titanium  and 
Columbiurn,  the  next  eight  substances,  are  metals,  for  the  most 
part  obtained  by  elaborate  processes  i>om  rare  mineral  productions. 
The  most  important,  as  well  perhaps  as  the  most  abundant  of 
these  substances,  is  chromium,  the  compounds  of  which,  from  the 
splendour  of  their  colours,  have  been  lately  much  employed  in 
the  arts.  It  may  be  remarked  of  all  these  substances,  that  at  pre- 
sent their  use  in  the  economy  of  nature  is  quite  unknown  to  us. 

(24)  (2.5)  Potassium  and  Sodium  are  the  metallic  bases  of  the 
two  well-known  alkaline  substances,  potash  and  soda,  which  are 
compounds  of  these  metals  with  oxygen.  Such,  however,  are 
the  powerful  aflinities  of  the  metallic  bases  for  oxygen,  that  they 
nowhere  exist  naturally  upon  the  surface  of  our  globe.  The  same 
may  be  also  remarked  of  potash  and  soda,  the  powerful  alkaline 
properties  of  which  prevent  them  from  existing  separately.     In 


LITHIUM.      CxVLCIUM.  81 

this  respect,  tlie  compounds  these  metals  form  with  oxygen,  pre- 
sent a  striking  confrnst  with  the  compounds  they  form  with  the 
analogous  principle,  chlorine  ;  the  compounds  of  potassium  and 
sodium  with  chlorine  (the  latter  of  which  constitutes  common 
salt,)  are  remarkable  for  their  fixed  and  permanent  character,  and 
for  the  little  tendency  in  general  which  they  have,  to  enter  into 
a  further  state  of  combination.  Besides  their  remarkable  avidity 
for  oxygen,  potassium  and  sodium  possess  some  other  unusual 
properties.  Potassium,  for  example,  is  so  light,  that  were  it  com- 
patible with  water,  it  would  swim  on  the  surface  of  that  fluid  ;  a 
circumstance  we  can  hardly  imagine  to  happen  with  a  metal.  Pot- 
ash and  soda  in  all  their  forms  are  most  important  principles,  and 
evidently  are  necessary  to  the  existence  of  the  present  order  of  things, 
both  mineral  and  organized  ;  for  there  are  few  organized  beings  that 
do  not  contain  more  or  less  of  them,  especially  of  soda.  Potash  is 
found  more  particularly  in  plants,  but  exists  also  in  animals  ;  while 
the  universal  presence  of  soda  in  animals,  in  the  form  of  common 
salt,  has  been  already  referred  to,  and  is  generally  known.  These 
alkalies  present  us  with  a  beautiful  instance  of  adaptation,  for  the 
purposes  which  they  seem  destined  to  fulfil  in  the  operations  of 
nature.  Had  they  been  solids,  or  had  they  formed  solid  com- 
pounds, like  many  of  the  preceding  principles,  they  would  have 
been  totally  unfitted  for  their  peculiar  office,  that  is  to  say,  for 
forming  a  constituent  element  of  the  fluids  of  organized  beings. 

(26)  Lithium  is  the  metallic  basis  odilhia,  a  substance  recently 
discovered,  and  intermediate  in  its  properties  between  the  alkalies 
and  the  earths  to  be  next  considered.  It  has  hitherto  been  met 
with,  in  some  rare  minerals,  in  small  quantities  only. 

(27)  Calcium,  the  metallic  bases  of /ime,  can  be  obtained  only 
by  a  troublesome  and  difficult  process,  and  of  course  does  not 
exist  naturally.  It  is  a  white  metal  like  silver,  and  by  union  with 
oxygen  is  readily  convertible  into  lime.  This  well  known  prin- 
ciple exists  in  the  greatest  abundance  in  nature,  not  as  quick-lime, 
but  united  with  carbon  and  oxygen,  in  the  form  of  common  lime- 
stone, marble,  &c.  The  great  importance  of  lime  in  the  economy 
of  nature  is  too  obvious  to  require  notice,  and  it  is  only  necessary 
to  revert  to  the  fact  that  this  earth  is  one  of  the  very  few  mineral 
productions  capable  of  forming  a  part  of  a  living  organized  being; 
at  least  in  any  quantity.  This  earth,  as  formerly  noticed,  con- 
stitutes \\\\\\  phosphorus  and  oxygen,  the  basis  of  the  bones  of  ani- 
mals ;  and  with  carbon  and  oxygen,  all  the  endless  variety  of  shells 
and  similar  products.  Thus  the  properties  of  lime  furnish  another 
striking  instance  of  adaptation  to  a  particular  purpose.  The  com' 
pounds  of  potash  and  soda  are  all  very  soluble  in  water,  and  hence 
are  chiefly  confined  to  x\\ejluids  of  animals,  in  which  their  pre- 


82  CHEMISTRY. 

sence  is  indispensable.  But  a  solid  frame-work  or  skeleton  was 
necessary  to  the  existence  of  the  more  perfect  animals,  and  as  this 
could  not  be  formed  from  the  soluble  potash  or  soda,  the  intro- 
duction of  another  mineral  substance  possessed  of  the  requisite 
properties  was  necessary.  Now  lime,  some  of  the  compounds 
of  which  are  solid  and  some/Iuld,  is  admirably  adapted  for  the 
purpose ;  and  lime  accordingly  has  been  chosen :  the  lime  is  car- 
ried, in  a  state  of  solution,  to  the  spot  where  it  is  required,  and  is 
there  converted  into  a  solid  ;  while  by  the  same  agency,  when 
necessary,  this  solid  is  a^ain  converted  into  a  fluid  and  removed ! 
It  seems  impossible  to  conceive  arrangements  to  present  more 
striking  evidences  of  adaptation  than  these  ;  and  the  more  we  con- 
sider the  subject  in  all  its  bearings,  the  more  wonderful  does  it 
appear. 

(28)  Magnesium  is  the  metallic  basis  of  the  well-known  earth 
called  magnesia.  It  is  said  to  resemble  calcium  in  its  properties, 
and  like  that  principle  does  not  exist  naturally,  at  least  upon  the 
surface  of  our  globe.  Magnesia,  though  occurring  most  abun- 
dantly in  nature,  and  entering'  very  largely  into  the  composition 
of  rocks,  does  not,  like  lime,  constitute  masses  of  great  extent  in 
the  same  simple  state  of  combination;  that  is  to  say,  there  are 
no  mountains  of  magnesia,  as  there  are  of  chalk  and  of  limestone. 
Magnesia,  even  more  decidedly  than  the  three  preceding  mine- 
ral substances,  seems  to  be  necessary  to  the  existence  of  orga- 
nized beings  ;  as  there  does  not  appear  to  be  one,  in  which  traces 
of  this  earth  are  not  met  with,  generally  associated  with  phos- 
phorus. Its  uses,  however,  are  less  obvious  than  those  of  the 
three  other  substances,  and  indeed  may  be  said  to  be  unknown ; 
though  there  is  reason  to  believe  that  it  is  most  intimately  con- 
nected with  the  vital  operations  of  organized  beings. 

(29)  (30)  Sfrontiiim,  and  Ban/wn,  the  metallic  bases  of  the 
two  earthy  bodies  strontla  and  barijfa,  arc  allied  to  calcium  and 
magnesium  in  some  of  their  properties,  but  differ  exceedingly 
from  them  in  others.  Their  combination  with  oxygen  exhibit 
still  more  decidedly  alkaline  powers  than  those  of  either  calcium 
or  magnesium,  and  in  consequence,  like  them,  they  only  exist 
in  various  states  of  combination ;  and  most  usually  with  carbon 
and  oxygen,  or  with  sulphur  and  oxygen.  Compared  with  lime 
and  magnesia,  strontia  and  baryta  exist  but  sparingly,  and  neither 
of  them  has  anything  to  do  with  organization  ;  indeed  many  of 
the  combinations  of  baryuni  are  virulent  poisons. 

(.31)  Miiminum  is  the  metallic  basis  of  the  earth  alumina,  the 
characteristic  ingredient  of  the  well  known  salt  called  «/i/m.  The 
metallic  basis,  like  the  preceding,  nowhere  exists  ;  but  alumina, 
the  compound  of  aluminum  and  oxygen,  is  one  of  the  most  abun- 


GLUCINUM,  YTTRIUM,  ETC.       IRON.  83 

dant  productions  of  nature,  and  constitutes  an  ingredient  in  by 
far  the  greater  number  of  rocks  and  soils  upon  the  surface  of  the 
globe.  The  difierent  kinds  of  clay,  also,  of  which  bricks,  earth- 
enware, &c.,  are  formed,  consist  chiefly  of  this  earth  in  difierent 
states  of  purity  ;  so  that  it  is  a  substance  of  great  utility  and  im- 
portance. Alumina  appears  to  have  nothing  to  do  with  organi- 
zation ;  at  least  it  is  not  known  to  form  a  necessary  constituent 
of  any  organized  being,  either  vegetable  or  animal ;  though  it  is 
in  constant  communication  with  organized  beings,  and  appears 
to  be  almost  necessary,  in  some  indirect  way,  to  their  existence. 
This  fact  is  very  remarkable  ;  for  as  the  earth  does  not  appear 
to  be  poisonous,  it  could  scarcely  have  been  so  completely  ex- 
cluded from  living  bodies,  except  by  some  design  beyond  our 
comprehension. 

(32)  (33)  (34)  (35)  Glucinum,  Yttrium,  Zirconium,  and 
Thorinum,  the  four  next  elementary  principles  are  the  metallic 
bases  of  substances,  usually  considered  as  possessing  the  charac- 
ters of  earthy  bodies,  and  denominated  Glucina,  Ittria,  ZirconiOj 
and  Tlioriaa.  They  all  appear  to  exist  very  sparingly  in  nature, 
and  are  only  met  with  in  some  rare  minerals.  Glucina  has  been 
hitherto  met  with  only  in  the  precious  stones  denominated  the 
emerald,  the  beryl,  and  the  euclase;  yttria  and  thorina  in  some  rare 
Swedish  and  Norwegian  minerals  ;  and  zirconia  in  the  jargon 
or  zircon  from  Ceylon,  and  in  the  hyaci?ith.  These  earths  more 
nearly  resemble  alumina  than  any  other  substance. 

(36)  /ron,  one  of  the  most  important,  is  also  one  of  the  most 
abundant  principles  in  nature.  It  is  met  with  occasionally  in  the 
metallic  state,  but  most  generally  it  is  found  mineralized  in  vari- 
ous ways,  and  can  only  be  obtained  pure  by  an  elaborate  process. 
Iron  exists  in  minute  quantities  in  almost  all  vegetable  and  animal 
products,  particularly  in  the  blood;  though  its  mode  of  combi- 
nation, as  well  as  its  precise  use,  are  quite  unknown.  Iron  may 
justly  be  considered  as  the  most  useful  of  all  the  metals,  and  the 
one  that  has  perhaps  contributed  more  towards  the  civilization  of 
mankind  than  any  other.  To  form  some  idea  of  its  use,  we  have 
only  to  reflect  what  would  happen  if  it  were  annihilated.  What 
substitute  could  be  found  for  it  in  all  the  numerous  instances  in 
which  it  contributes  to  the  wants  or  to  the  comforts  of  mankind; 
particularly  through  the  medium  of  tools,  of  almost  every  one  of 
which  it  constitutes  the  essential  material.  In  short,  when  we 
contemplate  all  the  circumstances  connected  with  this  metal,  its 
abundance,  the  manner  in  which  it  is  mineralized,  and  the  occa- 
sion which  it  thus  gives  to  human  ingenuity  to  extract  it  from  its 
ores  ;  its  wholesomeness  (for  many  of  the  metals  are  poisonous) ; 
its  properties,  particularly  its  extraordinary  tenacity  ;  its  strength, 


84  CHEMISTRY. 

its  property  of  welding,  of  being  converted  into  steel,  and  in  this 
form  of  being  tempered  to  any  degree  of  hardness  we  choose  ; 
its  magnetic  properties,  &:c., — when  we  contemplate  all  these 
circumstances,  it  is  impossible  not  to  be  struck  with  such  varied 
usefulness,  and  to  consider  iron,  not  only  as  an  article  evidently 
designed  for  the  benefit  of  man,  but  as  the  instrument  by  which 
he  should  conquer  and  govern  the  world  ;  and  thus  be  enabled  to 
place  himself,  where  it  was  evidently  intended  he  should  be,  at 
the  head  of  the  creation. 

(37)  Manganese  somewhat  resembles  iron  in  a  few  of  its  pro- 
perties. It  may  be  obtained  from  its  ores  by  an  elaborate  process, 
but  in  this  form  it  is  little  known  or  used.  Mangfanese  exists  in 
minute  quantities  in  certain  mineral  waters,  and  in  a  few  animal 
products  ;  and  its  combinations  with  oxygen,  are  not  only  em- 
ployed in  the  arts,  but  by  the  die  mist,  who  frequently  procures 
oxygen  for  his  experiments  from  the  ores  of  manganese.  Though 
much  diffused,  manganese  is  not  a  very  abundant  metal,  at  least 
compared  with  iron,  and  its  uses  in  the  economy  of  nature  are 
apparently  much  less  important. 

(38)  (39)  Nickel  and  Cobalt,  are  two  metals  somewhat  re- 
sembling each  other  in  a  few  of  their  properties,  and  their  ores 
are  often  associated  in  nature.  It  is  remarkable  also  that  they 
are  both  generally  found  combined  with  iron  in  those  bodies, 
which  occasionally  fall  from  the  atmosphere,  and  which  are  con- 
sidered as  of  meteoric  origin.  Like  iron  also  both  these  metals 
are  capable  of  becoming  magnetic.  Cobalt  is  used  in  the  arts, 
and  is  the  basis  of  the  blue  colour  upon  our  earthenware  ;  but 
neither  this  metal  nor  nickel  are  to  be  compared  with  iron  in 
point  of  utility,  nor  are  they  very  abundant  productions. 

(40)  Cerium  is  a  metal  very  little  known,  and  has  hitherto 
been  obtained,  in  minute  quantities  only,  from  some  rare  minerals 
occurring  in  Sweden  and  in  Greenland. 

(41)  (42)  Zinc,  Cadmium.  These  two  metals  are  generally 
associated  in  nature,  and  somewhat  resemble  each  other  in  eitrh 
properties  ;  but  the  last  is  comparatively  much  less  abundant,  and 
has  been  only  recently  discovered.  Zinc  is  a  metal  easily  fusible, 
of  a  bluish  white  colour,  and  of  a  lamellated  brittle  texture; 
though  by  peculiar  management  it  may  be  rendered  malleable. 
It  is  an  ingredient  in  the  well-known  compound  metal,  brass, 
and  in  this  form  is  much  used  and  is  of  considerable  impor- 
tance. 

(43)  Lead.  This  well-known  metal  is  not  found  in  its  metal- 
lic state,  but  its  ores  are  very  abundant,  and  most  of  the  lead  of 
commerce  is  extracted  from  the  mineral  called  galena,  which  is 
a  compound  of  lead  and  sulphur.     The  general  properties  of  lead 


TIN.       BISMUTH.       COPPER.       MERCURY.       SILVER,  GOLD.         85 

and  of  its  compounds  render  it  of  considerable  importance ;  but 
its  poisonous  properties  are  a  considerable  draw-back  to  its  use- 
fulness. Why  lead,  and  other  mineral  matters,  should  have  been 
constituted  poisonous  is  a  question  beyond  our  reach  ;  and  all 
we  can  at  present  venture  to  state  on  this  and  on  similar  points  is, 
that  it  is  not  actually  necessary  that  man  should  employ  lead  or 
other  poisons,  and  that  he  may,  if  he  chooses,  avoid  their  dele- 
terious properties. 

(44)  Tin.  This  useful  metal  has  been  employed  by  man  from 
the  most  remote  antiquity,  though  it  nowhere  exists  naturally 
in  its  metallic  state,  but  usually  in  conjunction  with  oxygen.  Tin 
is  not  a  very  abundant  metal,  being  apparendy  confined  to  a  few 
localities  only,  one  of  the  most  noted  of  which  is  Cornwall.  It 
is  much  used  in  the  arts,  and  hence  is  of  considerable  importance. 

(45)  Bismuth  occurs  in  nature  both  in  the  metallic  state  and 
in  various  states  of  combination.  It  has  a  reddish  white  colour 
and  a  lamellated  brittle  texture,  and  is  easily  fusible.  Bismuth  is 
not  a  very  abundant  metal,  and  is  not  much  employed. 

(46)  Copper  occurs  in  nature  in  the  metallic  state,  but  much 
more  frequently  mineralized,  especially  with  sulphur.  The  valua- 
ble properties  of  copper,  both  in  its  pure  and  mixed  state,  render 
it  of  considerable  importance  ;  and  it  is  in  consequence  much  em- 
ployed in  the  arts.  With  zinc  it  constitutes  brass ;  with  tin  bell- 
metal ;  hoi\\  well-known  compounds.  Copper  has  been  lately 
said  to  exist  in  very  minute  quantities  in  organic  nature,  but  whe- 
ther as  an  accidental,  or  as  an  essential  ingredient  is  not  known. 
The  compounds  of  copper  are  poisonous,  but  these  poisonous  pro- 
perties, like  those  of  lead,  can  be  easily  obviated  and  guarded 
against. 

(47)  Mercury.  This  well-known  fluid  metal  occurs  in  the 
metallic  state,  but  more  frequently  mineralized,  especially  with 
sulphur.  Its  importance  in  the  arts,  and  as  a  medicinal  agent,  are 
too  well  known  to  require  mention  here.  The  fluidity  of  mercury 
presents  a  beautiful  instance  of  the  endless  diversity  of  nature,  and 
adds  much  to  its  importance  and  usefulness.  Mercury  exists  in 
considerable  abundance,  though  much  less  so  than  many  of  the 
preceding  elementary  principles. 

(48)  (49)  Silver  and  Gold,  and  their  uses,  are  too  familiar  to 
require  enumeration.  Tiiey  are  both  met  wiUi  in  the  metallic 
state,  but  silver  also  occurs  mineralized.  So  unimportant  a  part 
do  they  seem  to  perform  in  the  economy  of  nature,  that  if  they 
were  annihilated,  it  is  probable  that  the  world  would  go  on  just 
as  well  without  them.  How  different  in  these  respects  from  iron, 
and  how  much  less  therefore  intrinsically  valuable  !  Indepen- 
dently of  their  beauty,  the  only  really  valuable  properties  of  silver 

8 


86  CHEMISTRY. 

and  gold  are  the  difficulty  with  which  they  are  acted  on  by  heat 
and  other  extraneous  agents,  properties,  which  if  they  were  more 
abundant,  would  render  them  well  adapted  for  a  great  many  use- 
ful purposes. 

(50)  (51)  (52)  (53)  (54)  Platinum,  Palladimn,  FJiodium,  Iri- 
dium, and  Osmium,  are  metallic  substances  usually  found  asso- 
ciated in  small  quantities,  chiefly  in  certain  districts  of  South 
America,  but  recently  also  in  the  old  world.  Platinum,  the  most 
abundant  and  important  of  them,  is  the  heaviest  body  in  nature. 
It  is  scarcely  acted  on  by  any  ordinary  agents,  but  it  may  be 
welded  by  heat  ;  properties  which  render  it  exceedingly  valuable 
for  many  purposes,  and  make  us  regret  that  it  is  not  more  abun- 
dant. Palladium  somewhat  resembles  platinum  in  its  i^roperties, 
but  occurs  in  less  quantity.  The  other  three  metals  exist  in  very 
minute  quantities,  and  their  properties  are  very  little  known. 

We  have  thus  taken  a  summary  view  of  the  different  elementary 
principles  met  with  upon  the  surface  of  our  globe,  and  of  their 
leading  compounds  ;  and  we  are  now  to  consider  the  laws  which 
regulate  the  union  of  these  principles  with  one  another. 


Section  II. 
Of  the  Laws  of  Chemical  Combination. 

As  the  following  remarks  upon  the  laws  of  chemical  combination 
can  scarcely  be  so  given  as  to  prove  a  source  of  interest  to  the 
general  reader,  he  is  desired  to  pass  them  over  and  to  turn  to  the 
last  section  of  the  present  chapter,  where  he  will  find  a  brief  re- 
capitulation of  the  leading  facts,  and  of  the  arguments  which  they 
furnish  in  favour  of  design,  and  of  the  wisdom  and  power  of  the 
Creator. 

In  the  preceding  chapter  we  advanced  a  few  of  the  leading  ar- 
guments which  induce  us  to  adopt  the  hypothesis  that  all gaseotis 
bodies  under  the  same  pressure  and  temperature,  contain  an 
equal  number  of  self-repulsive  molecules ;  and  we  have  now  to 
consider,  very  briefly,  some  of  the  important  consequences  to 
which  this  hypotliesis  naturally  leads. 

It  seems  to  be  satisfactorily  establislied  that  bodies,  in  their  ga- 
seous state,  combine  both  chemicallij  and  coheslveli/  with  refer- 
ence to  their  volumes  ;  that  is  to  say,  that  the  same  volume  of  a 
gas  always  combines  with  either  precisely  a  similar  volume  of  the 
same  or  of  another  gas,  or  with  some  multiple  or  submultiple  of 
that  gas  (in  other  words  with  twice,  or  thrice,  or  half,  or  a  quarter 
as  much,  &;c.)  but  not  with   any  intermediate   proportion ;  and 


LAWS  OF  CHEMICAL  COMBINATION.  87 

further,  that  the  resulthig  compound  always  has  reference  by  vo- 
lume to  the  original  volumes  of  its  constituent  elements.  Let  us 
take  water  for  example.  Water  has  been  shown  to  consist  of  one 
volume  of  oxygen  gas,  and  two  volumes  of  hydrogen  gas  ;  and  so 
invariably,  that  we  cannot  suppose  water  to  be  formed  of  any  other 
proportions  of  these  elements.  It  has  been  also  shown  that  the 
resulting  water,  if  in  the  state  of  steam,  occupies  exactly  the  space 
of  two  volumes,  so  that  one  volume  has  disappeared.  Now  let 
us  consider  attentively  what  must  have  happened  during  these 
changes.  One  volume  of  oxygen  gas  has  contributed  to  form  two 
volumes  of  water,  which  two  volumes  of  water,  according  to  our 
hypothesis,  must  consist  of  twice  the  number  of  self-repulsive 
molecules  contained  in  the  one  volume  of  oxygen  ;  yet  every  one 
of  these  molecules  must  contain  oxygen,  because  oxygen  is  an  es- 
sential element  of  water :  it  follows,  therefore,  irresistibly,  that 
every  self-repulsive  molecule  of  oxy gen  has  been  divided  into  two, 
and  consequently  must  have  originally  consisted  of  at  least  two 
elementary  molecules,  somehow  or  other  associated,  so  as  to  have 
formed  only  one  self-repulsive  molecule.  This  conclusion,  which 
seems  to  flow  naturally  from  our  premises,  is  most  important, 
as  we  shall  see  immediately,  and  enables  us  to  throw  no  small 
light  upon  many  points  deemed  obscure.  In  the  mean  time  let  us 
consider  briefly  the  nature  of  the  compound  self-repulsive  mole- 
cule of  oxygen. 

We  endeavoured  to  show  in  the  previous  chapter,  that  every 
ultimate  molecule  of  matter  must  possess  two  kinds  of  polarity, 
which,  for  want  of  better  terms,  we  denominated  the  chemical  and 
the  cohesive  ;  and  that  these  polarities  bear  the  same  relations  to 
each  other  as  electricity  and  magnetism ;  in  other  words  that,  like 
these  forces,  the  polarities  exist  at  right  angles  to  each  other. 
Hence  if  a  and  b  be  supposed  to  be  two  molecules  of  oxygen,  of 
which  Ee  Ee  represent  the  chemical  poles  and  axis,  and  mm,  mm  the 
cohesive,  it  is  evident  that  these  two  molecules  may  be  supposed 
to  combine  in  two  ways,  either  e  to  e  chemically,  or  m  to  m  co^ 
hesively  ;  but  the  latter  form  of  course  is  most  probable yVom  the 
sitnilar  nature  of  the  molecules.*     Every  self-repulsive  molecule 

•  The  general  and  strong'  analogy,  if  not  identity,  in  all  respects  except 
direction,  between  the  axial  and  the  equatorial  forces,  has  been  already 
alluded  to,  and  is  exemplified  by  the  striking  resemblance  between  elec- 
tricity and  magnetism.  We  have  seen  also  that  in  the  crystallized  state, 
similar  molecules  probably  combine  chemically.  Hence,  although  the  rule 
stated  in  the  text  be  true,  that  similar  molecules  only  combine  cohesively  ; 
yet  there  may  be,  and  probabl}^  are,  instances  in  which  they  combine  che- 
mically.  For  the  same  reasons,  dissimilar  molecules  may  also  occasionally 
combine  cohesively.  It  is  probable  that  such  states  of  combination  might 
be  readily  detected  by  the  optical  properties,  or  by  some  other  peculiarity 


88  CHEMISTRY. 

of  oxygen,  therefore,  as  it  exists  in  a  state  of  gas,  must  consist 
oi  at  least  two  molecules,  united  to  each  oiher  cohesively,  and 
acting  as  a  single  one  ;  and  the  same  may  be  sliown  with  respect 
to  other  gaseous  bodies,  as,  for  instance,  hydrogen.  It  cannot, 
indeed,  be  inferred  from  the  composition  of  water,  as  above  stated, 
whether  the  self-repulsive  molecule  of  hydrogen  be  double  or  not; 
but  this  may  be  demonstrated  from  other  compounds  into  which 
hydrogen  enters.  Tlius  muriatic  acid  gas  is  composed  of  one  vo- 
lume of  chlorine  and  one  volume  of  hydrogen,  which  unite  with- 
out any  condensation,  and  form  two  volumes  of  muriatic  acid  gas  ; 
now  in  this  case,  it  is  evident  that  not  only  the  self-repulsive  mole- 
cule of  hydrogen,  but  also  that  of  the  chlorine,  must  be  double  at 
least,  like  the  molecule  of  oxygen  above  mentioned  ;  and  the  same 
might  be  shown  with  respect  to  the  other  gaseous  bodies. 

We  have  said  above  that  the  self-repulsive  molecules  of  oxygen 
and  of  hydrogen  are  at  least  double;  but  the  probability  is  that 
they  are  in  reality  much  more  compounded,  as  the  following  ob- 
servations will  show.  The  self-repulsive  molecule  of  water,  on 
entering  into  combination,  is  often  found  to  be  divided  into  two 
or  three  (perhaps  more)  parts.  Now  as  we  cannot  admit  the  di- 
vision of  an  ultimate  molecule  or  atom,  we  must  of  course  con- 
clude that  the  molecules  of  oxygen  and  of  hydrogen  are  much 
more  compounded  than  as  above  represented,  and  must  each  of 
them  contain  at  least  three  component  or  sub-molecules.  Hence 
the  self-repulsive  molecules  of  water  will  consist  of  at  least  nine 
component  sub-molecules  (viz.  three  of  oxygen  and  six  of  hydro- 
gen) which  we  may  suppose  to  be  associated, — in  the  first  place 
the  hydrogen  with  the  oxygen,  chemically ;  and  afterwards  the 
three  sub-molecules  of  water  with  one  another  cohesively,  so  as 
to  constitute  one  spheroidal  molecule  ;  in  a  manner  that  with  a 
little  ingenuity  it  would,  perhaps,  not  be  difficult  to  represent 
mechanically.* 

Precisely  the  same  laws  of  union  may  be  supposed  to  prevail 
among  the  molecules  of  bodies  themselves,  as  they  actually  exist 
around  us,  Tiuis  let  us  take  the  crystal  of  oxahc  acid  as  an  in- 
stance for  illustration.  This  acid  is  composed,  according  to  the 
present  language  of  chemists,  of  two  molecules  of  carbon,  and 

in  the  physical  properties  of  bodies,  if  in  a  crystalline  form ;  but  by  no 
other  known  means.  Do  not  some  of  the  phenomena  of  Isomerism,  that 
is  to  say,  the  property  wliich  the  same  body  occasionally  possesses  of  as- 
suming" different  forms,  dejjend  upon  tliese  cliang^es  ? 

•  When  bodies,  as,  for  example,  water,  arc  subjected  to  intense  degrees 
of  heat,  it  is  not  improbable  that  in  many  instances  the  self-rcpulslvc  mole- 
cules are  more  or  less  separated  into  their  constituent  sub-molecules  ; 
in  whicli  case  of  course  the  bodies  may  be  supposed  to  exhibit  altogether 
different  clastic  powers  and  laws  of  expansion. 


LAWS  OF  CHEMICAL  COMBINATION.  89 

three  of  oxygen,  which  by  combining,  form  the  acid ;  while,  to 
complete  the  compound  molecule,  and  to  adapt  it  for  crystallization, 
three  molecules  of  water  are  required  to  be  somehow  associated 
with  each  of  the  molecules  of  the  acid.  Now  in  this  case,  we 
suppose,  that  the  two  molecules  of  carbon  (each  of  which  is  per- 
haps already  made  up  of  several  sub-molecules)  are  associated 
together  into  one  symmetrical  super-molecule  ;  that  the  three 
molecules  of  oxygen  are  arranged  in  a  similar  manner,  and  then 
associated  chemically  with  the  super-molecule  of  carbon,  and  thus 
form  by  their  union  a  molecule  of  oxalic  acid  ;  finally,  that  the 
three  molecules  of  water  are  united  into  one  super-molecule,  which 
combines  chemically  with  the  molecule  of  oxalic  acid,  and  thus 
completes  the  molecule  of  the  acid  as  it  actually  exists  in  the 
crystalline  form. 

Such  are  the  vieM^s  we  have  been  induced  to  take  of  the  nature 
of  chemical  combination,  and  whether  right  or  wrong,  they  have 
the  merit  of  being  exceedingly  simple  and  consistent  with  them- 
selves throughout,  which  can  hardly  be  said  of  any  others  with 
which  we  are  acquainted.  Indeed  much  reflection  upon  the  sub- 
ject, for  many  years  past,  has  satisfied  us  that  chemical  combina- 
tions can  be  rationally  explained  only  in  some  such  manner  as 
we  have  supposed.  Any  lengthened  argument,  however,  upon 
the  laws  of  chemical  combination  here,  would  be  quite  out  of 
place ;  we  shall  therefore  confine  ourselves  to  the  following  ob- 
servations. 

1.  The  above  view  of  the  molecular  constitution  of  bodies  na- 
turally suggests  the  important  question  :  do  the  sub-molecules, 
which  we  suppose  to  unite  together  cohesively  and  form  the  self- 
repulsive  molecule,  of  oxygen  and  hydrogen  for  instance,  possess 
the  same  properties  as  those  of  oxygen  and  hydrogen,  or  do  they 
possess  different  properties  ?  This  question,  in  most  instances, 
cannot,  in  the  present  state  of  our  knowledge,  be  satisfactorily 
answered  ;  though  there  is  every  reason  to  believe  that  the  pro- 
perties both  of  the  sub-molecule  and  of  the  super-molecule  gene- 
rally differ  from  those  of  the  molecule  itself,  but  that  the  differences 
are  rather  of  a  specific  than  of  a  generic  character.*  Thus  che- 
mists have  shown  that  different  volumes  of  the  same  gaseous 
body,  termed  carburetted  hydrogen,  combine  together  and  form 
various  compounds  :  we  have,  for   example,  a  gas,  one  volume 

*  What  we  term  the  sensible  properties  of  bodies  are,  of  course,  in  all 
instances,  the  result  of  a  g-reat  number  of  molecules  acting"  tog-ether  at 
the  same  time  ;  hence  below  a  certain  point,  mere  difference  of  numbers 
may  be  supposed  to  produce  a  change  in  sensible  properties,  not  only  in 
degree,  but  in  kind  :  of  the  sensible  properties  of  a  single  molecule  we 
can  form  no  conception. 

8* 


90  CHEMISTRY. 

of  which  contains  two  volumes  of  carburetted  hydrogen  ;  another, 
one  vohime  of  which  contains  three,  and  another  four,  of  the 
same  gaseous  body.  Now  the  sensible  properties  of  all  these 
compounds,  though  resembling  each  other  in  some  respects,  are 
yet  specifically  different;  and  as  they  are  all  composed  of  the 
same  gaseous  body  in  different  proportions,  these  differences 
must  be  considered  rather  as  the  result  of  cohesive  than  of  che- 
mical union.  Thus  the  supposition,  that  both  the  sub-molecules 
and  the  super-molecules  of  bodies  may  possess  properties  differ- 
ent from  one  another  and  from  the  standard  molecule,  is  rendered 
exceedingly  probable  by  the  above  f\icts  ;  and  if  our  space  ad- 
mitted, it  would  not  perhaps  be  difficult  to  bring  forward  other 
facts  of  the  same  kind.  This  however,  would  be  foreign  to  our 
purpose  ;  and  we  shall  only  remark,  that  a  great  many  curious 
circumstances,  at  present  but  very  imperfectly  understood,  evi- 
dently appear  to  be  referrible  to  a  similar  principle. 

2.  Although  we  have  thus  rendered  it  exceedingly  probable  that 
the  molecules  of  bodies  considered  at  present  as  elementary,  are 
immediately  compounded  of  many  others  more  or  less  resembling 
them;  yet  it  is  obvious  that  there  must  be  a  point  at  which  these 
and  other  elements  exist  in  a  primary  or  ultimate  form,  and  be- 
yond which,  if  they  can  be  supposed  to  be  subdivided,  they  must 
become  something  altogether  different.  In  this  respect,  therefore, 
the  views  we  have  advanced  accord  generally  with  those  at  pre- 
sent entertained  ;  and  the  only  point  in  which  they  differ,  is  in  sup- 
posing that  the  self-repulsive  molecule,  as  it  exists  in  the  gaseous 
form,  does  not  represent  the  ultimate  molecule,  but  is  composed 
of  many  of  them.  With  respect  to  the  nature  of  the  ultimate  sub- 
molecules  of  those  bodies  which  we  consider  at  present  as  ele- 
ments, as,  for  instance,  of  oxygen,  they  may  naturally  be  supposed 
to  possess  the  most  intense  properties  or  polarities.  Indeed  such 
sub-molecules  may  be  imagined  to  resemble  in  some  degree  the 
imponderable  matters,  heat,  &;c.,  not  only  by  their  extreme  te- 
nuity, but  in  otlier  characters  also;  and  this  very  intensity  of  pro- 
perly and  cliaracter  may  be  reasonably  considered  as  one,  if  not  the 
principal  reason,  why  they  are  incapable  of  existing  in  a  detached 
form.  Lastly,  are  not  these  ultimate  and  refined  forms  of  matter 
extensively  employed  in  many  of  the  operations  of  nature,  and 
particularly  in  many  of  the  processes  of  organization? 

3.  By  supposing  that  these  laws  of  combination  are  not  con- 
fined to  elementary  bodies,  but  extend  to  all  others  throughout  na- 
ture; and  that  ])0(lies,  however  complicated  they  may  be,  always 
combine  with  reference  to  their  volume  in  the  gaseous  slate,  and 
always  act  as  simple  molecules;  we  are  enabled  in  some  de- 
gree to  explain  that  endless  variety  of  property  and  condition 


LAWS  OF  CHEMICAL  COMBINATION.  91 

which  we  see  around  us.  For  no  sooner  is  a  new  compound 
molecule  formed  by  an  assemblage  of  similar  molecules,  than  it 
may  be  supposed  to  be  capable  of  combining  witli  other  molecules 
chemically^  and  of  thus  entering  into  a  long  and  novel  series  of 
combinations;  while  these  combinations  again  in  their  turn  may 
be  imagined  to  lead  to  others,  and  so  on,  till  the  variety  becomes 
extreme.  Indeed  v/ere  not  such  combinations  limited  by  the  very 
nature  of  things  themselves,  no  two  substances  would  probably 
possess  the  same  properties.  As  it  is,  most  of  these  compounds 
are  incapable  of  separate  existence;  thus  the  compound  super- 
molecules  of  water  in  the  crystal  of  oxalic  acid  before  referred  to, 
are  incapable  of  separate  existence  :  if  they  could  exist  separately, 
would  they  assume  the  form  of  water? 

4.  It  would  not  be  diflicult,  though  perhaps  not  very  safe  or 
prudent  in  the  present  state  of  our  knowledge,  to  speculate  on  the 
crystalline  forms  assumed  by  different  bodies,  with  reference  to 
the  principles  we  have  advanced.  We  shall  therefore  not  touch 
upon  this  part  of  the  subject,  further  than  by  observing  that  the 
cohesive  force,  though  supposed  to  possess  some  peculiarity  as 
existing  among  the  molecules  of  different  bodies,  is  nevertheless 
essentially  but  of  one  kind.  When  therefore  the  molecules  of 
different  bodies  are  of  the  same  size  (or  rather  of  the  same  weight,) 
they  may  be  naturally  supposed  capable  of  associating  themselves 
into  the  same  form  ;  and  if  they  happen  to  be  mixed  together,  they 
may  even  enter  indiscriminately  into  the  same  crystal.  Hence 
arises  what  has  been  termed  the  isomorphism  of  bodies  ;  while  if 
there  be  a  near  approximation,  but  not  an  exact  coincidence  in  the 
above  relations,  they  may  upon  the  same  principles  be  supposed 
to  give  origin  to  plesiomorphism,  that  is  to  say,  to  a  near  ap- 
proach to  a  similarity  of  form. 

5.  With  respect  to  the  nature  of  the  circumstances  which  deter- 
mine the  peculiar  characters  and  modes  of  existence  of  bodies  we 
know  very  little.  We  are  almost  equally  ignorant  also  of  the  na- 
ture of  the  causes  which  determine  the  cohesion  of  the  molecules 
of  bodies  into  the  crystalline  form.  A  variety  of  arguments  might, 
however,  be  brought  forward  which  appear  to  show  that  the  size 
and  shape  of  tlie  molecules  have  a  great  deal  to  do  with  crystalli- 
zation ;  certainly,  at  least,  the  molecules  must  be  supposed  to  have 
a  size  and  shape  somehow  or  other  adapted  for  the  modes  in  which 
they  are  arranged,  otherwise  they  could  not  be  capable  of  such 
an  arrangement.  The  cause  of  this  similarity  of  size  and  shape 
is  unknown,  but  it  most  probably  depends  upon  the  similarity  of 
iveight  [fsobarism)  of  the  molecule;  that  is  to  say,  upon  the  re- 
lation or  identity  of  the  absolute  quantify  of  matter  which  the 
molecule  contains ;  which  relation,  as  far  as  we  can  perceive,  is 


92  CHEMISTRY. 

not  only  the  sole  circumstance  common  to  the  molecules  of  dif- 
ferent bodies,  but  that  which  of  all  others  is  the  most  likely  to 
produce  identity  in  the  size  and  shape  of  these  molecules. 

6.  When  the  molecules  of  bodies  in  solution  do  not  happen  to 
possess  the  requisite  size  and  shape  for  cohesion,  there  is  from 
the  phenomena  every  reason  to  believe,  that  they  occasionally 
possess  the  power,  as  it  were,  of  making  up  the  necessary  form, 
by  attaching  to  themselves  the  molecules  of  other  bodies.  Now, 
bodies  so  attached  may  be  considered  as  acting  a  sort  of  comple- 
mentary part  ;  that  is  to  say,  they  may  be  supposed  to  complete 
the  figure  or  size  of  the  molecule,  so  as  to  adapt  it  for  combining 
in  a  certain  manner.  Thus  the  water  of  crystallization  (and  per- 
haps occasionally  other  matters)  appears  in  the  greater  number  of 
instances  to  perform  an  office  of  this  kind,  and  to  be  in  fact  strictly 
complementary  to  that  particular  figure  and  size  of  the  molecules, 
which  may  be  supposed  to  be  requisite  for  enabling  them,  not 
only  to  combine  the  more  readily  with  each  other,  but  at  the 
same  time,  to  form  a  symmetrical  solid  or  crystal.^ 

One  or  two  other  circumstances  connected  with  this  part  of 
our  subject  will  be  better  understood  after  we  have  considered  a 
little  more  in  detail,  the  combinations  of  bodies  with  reference 
to  their  iveights,  and  the  absolute  quantity  of  matter  which  they 
contain.  To  this  most  interesting  inquiry,  therefore,  we  shall 
in  the  next  place  proceed,  confining  ourselves,  however,  as  before, 
principally  to  tlie  elements  of  water,  hydrogen  and  oxygen. 

It  has  been  found  by  experiment  that  the  same  volumes  of  dif- 
ferent bodies  in  the  gaseous  state  have  very  different  weights. 
Thus  for  instance  a  volume  of  oxygen  weighs  sixteen  times  as 
much  as  the  same  volume  of  hydrogen.  Hence  as  the  number 
of  self-repulsive  molecules  in  each  of  these  gases  is  presumed  to 
be  the  same,  the  weight  of  the  self-repulsive  molecule  of  oxygen 
must  of  course  be  sixteen  times  greater  tlian  that  of  hydrogen; 
and  GENERALLY,  the  loeights  of  the  self-repulsive  molecules  of 
all  bodies  ivill  be  as  the  specific  gravities  of  these  bodies  in  the 
gaseous  state,  or  ivill  bear  certain  simple  relations  to  these  spe- 
cific gravities.     'J'his  relation  in  weight  among  the  molecules  of 

*  There  is  every  reason  to  befieve  that  one  variety  of  isomorpliism  is 
effected  on  the  principles  here  stated  ;  and  that  the  molecules  of  different 
substances,  by  atlructin.^-  to  themselves  different  quantities  of  v/atcr,  or  of 
other  matters,  may  ultimately  make  up  compound  molecules  similar  to 
those  of  the  bodies  with  which  they  may  happen  to  be  mixed,  and  may 
thus  enter  indiscriminately  with  these  bodies  into  the  crystalline  form. 
Such  a  stiite  of  things  is  calculated  to  baffle  the  mere  chemist,  however 
expert  ;  thoug-h  it  is  probable,  that  if  carefully  examined  and  understood, 
an  intermixture  of  this  kind  might  be  detected  by  the  optical  properties 
of  the  crystal. 


LAWS  OF  CHEMICAL  COMBINATION.  93 

bodies  constitutes  the  basis  of  what  is  called  the  Jiiomic  theory^ 
proposed,  some  years  ago  by  Dr.  Dalton,  who  established  the 
most  important  fact,  that  bodies  do  not,  as  formerly  supposed, 
combine  at  random,  but  in  definite  proportions  by  weight ;  and 
if  the  preceding  doctrines  be  well  founded,  it  is  evident  they  can- 
not combine  otherwise.*  As  however  water  is  composed  of  one 
volume  of  oxygen  united  with  two  volumes  of  hydrogen,  the  re- 
lative weights  of  the  hydrogen  and  oxygen  in  water  will  be,  not 
as  1  to  16,  but  as  1  to  8  only  ;  while  the  weight  of  tlie  self-re- 
pulsive molecule  of  steam  will  be  9.  Hence,  as  one  of  the  other 
of  the  elements  of  water  is  usually  made  the  basis  of  the  atomic 
numbers,  this  difference  between  the  volumes  and  the  combining 
weights  of  its  elements  has  produced  considerable  confusion,  and 
has  given  rise  to  much  needless  discussion.  As  a  mere  matter 
of  convenience  it  is  certainly  preferable  to  consider  the  two  vol- 
umes of  hydrogen  as  one  atom,,  (to  use  the  language  of  Dr.  Dal- 
ton), in  which  case  oxygen  will  be  8,  and  water  9 ;  but  a  strictly 
philosophical  arrangement,  supposing  the  principles  we  have 
advanced  be  well  founded,  would  require  that  the  volume  in  all 
instances  should  be  tnade  the  molecular  unit ;  in  which  case, 
the  relative  weights  of  the  self-repulsive  molecules  of  hydrogen 
and  oxygen,  as  above  mentioned,  will  be  as  1  to  IG. 

In  this  country  two  volumes  of  hydrogen,  as  we  have  said,  are 
usually  considered  as  one  atom.,  or  unity,  in  which  case  oxygen 
is  8  ;  but  some  have  chosen  instead  of  hydrogen,  to  make  oxy- 
gen unity  or  10,  in  which  case  hydrogen  of  course  will  be  the 
one-eighth  of  1  or  of  10,  that  is  to  say,  .125  or  1.25  ;  and  water, 
instead  of  9,  will  be  1.125  or  11.25.  It  matters  not  which  of 
these  series  of  numbers,  or  whether  any  other  be  employed,  so 
that  the  same  relative  proportions  be  observed  among  them  ;  but 
the  first  series  is  that  most  generally  adopted,  and  is  upon  the 
whole  the  most  convenient.  In  the  above  manner  the  atomic 
iveightSy  as  they  are  termed,  of  all  bodies  capable  of  assuming 
the  gaseous  form  can  be  easily  obtained  ;  but  in  those  bodies  that 
do  not  assume  the  gaseous  form,  in  their  simple  state,  but  in  some 
state  of  combination  only,  we  are  obliged  to  deduce  the  weight 
of  the  primary  molecule  from  that  of  the  compound.  Thus  car- 
bon in  its  elementary  state  is  incapable  of  assuming  the  gaseous 
form ;  but  combined  with  oxygen  it  forms  carbonic  acid  gas,  one 
volume  of  which  weighs  22  times  as  much  as  our  standard  two 
volumes  of  hydrogen.  Now  it  has  been  found  by  other  experi- 
ments, that  of  these  22  parts,  16  are  oxygen.     The  remaining  6 

*  The  reader  is  referred  lO  *'  An  Introduction  to  the  Atomic  Theory," 
recently  published  by  Dr.  Daubenv,  Professor  of  Chemistry,  at  Oxford, 
for  an  interesting-  and  able  inquiry  into  the  principles  of  this  theory. 


94  CHEMISTRY. 

must  therefore  be  carbon  ;  and  accordingly  6  is  the  number  upon 
our  scale  representing  carbon,  and  the  proportion,  with  reference 
to  which,  this  body  always  enters  into  composition.  In  the  case 
of  bodies,  as  for  instance,  lime,  which  are  incapable  of  assuming 
a  gaseous  form  either  alone  or  in  combination,  we  are  obliged  to 
trust  solely  to  analysis  ;  thus  common  marble  or  carbonate  of  lime, 
as  it  is  termed  by  chemists,  is  found  to  be  composed  of  22  parts 
of  carbonic  acid,  and  28  parts  of  lime ;  28  therefore  represents 
upon  our  scale  the  atomic  weight  of  lime,  and  so  of  all  others. 

It  may  be  observed  that  we  have  spoken  as  if  the  atomic  weights 
of  bodies  were  related  to  one  another  by  multiple  ;  that  is  to  say, 
were  all  multiples  of  some  common  unit.  Now  this  opinion  has 
been  maintained  by  somiC,  while  it  has  been  denied  l3y  others  ; 
who  admitting  that  multiples  in  weight  are  necessary  to  the  union 
of  the  same  body,  both  chemically  and  cohesively^  will  not  admit 
that  they  are  necessary  to  the  union  of  different  bodies.  The 
matter  is  one  that  in  the  present  imperfect  state  of  chemistry  can 
hardly  be  determined  by  experiment;  for  what  with  the  difhculty, 
or  rather  impossibility,  of  procuring  bodies  in  a  perfecdy  isolated 
form,  and  the  unavoidable  imperfections  of  all  chemical  processes, 
we  can  scarcely  hope  to  arrive  within  the  necessary  limits  of  pre- 
cision. If  the  above  views  of  molecular  relations  however,  be  well 
founded,  it  seems  almost  impossible  to  arrive  at  any  other  conclu- 
sion, than  that  the  combining  weights  of  all  bodies  are  intimately 
related  by  multiple;  though  to  enter  further  upon  the  subject  here 
would  be  quite  foreign  to  our  present  purpose.* 

Lastly,  it  may  be  remarked  that  the  numbers  at  present  con- 

*  For  the  sake  of  those  who  are  interested  in  such  matters,  one  or  two 
of  the  leading-  arg-umcnts  may  be  briefly  stated.  We  have  rendered  it 
probable  that  when  two  or  more  molecules  of  the  same  bod}'  combine  co- 
hesivelij,  they  form  a  compound,  wliich  thoug'h  having  properties  in  some 
degree  allied  to  those  of  the  original  molecule,  nevertlieless  usually  pos- 
sesses a  s])ecific  difference,  (that  is  to  say,  the  chemical  polarities  of  the 
compound  molecule  as  modified  by  the  union,  will  be  different  from  those 
of  the  simple  molecule).  But  a  body  possessing  a  specific  difference,  may 
be  supposed  to  be  a  new  body,  and  thus  capable  of  combining  in  future, 
not  cohesively,  but  chemically  with  our  original  molecule.  Now  in  such 
a  case  it  is  evident  that  the  weight  of  the  original  molecule  and  that  of  the 
new  compound  molecule  must  have  a  certain  relation  to  one  another  by 
multiple.  If  our  space  admitted,  it  would  not,  we  believe,  be  difficult  to 
point  out  instances  of  such  combination  among  chemical  phenomena  ;  but 
we  shall  merely  observe,  that  many  of  the  substances  at  present  considered 
as  elementary,  appear  to  be  constituted  upon  the  above  principles  from 
some  common  molecule  of  a  still  more  elementary  character.  Moreover 
this  law  seems  to  hold  universally  throughout  nature  ;  and  those  substances 
related  to  the  same  molecule,  in  general  constitute  a  natural  group  or  fa- 
mily, having  certain  properties  in  common. 


LAWS  OF  CHEMICAL  COMBINATION.  95 

ventionally  employed  by  chemists,  to  represent  what  have  been 
called  the  atomic  weights  of  bodies,  are  so  convenient  that  they 
will  not  readily,  nor  indeed  ought  lightly,  to  be  set  aside  ;  though 
there  is  reason  to  believe  that  many  of  them  require  revision,  and 
are  destined  to  undergo  material  alterations,  even  as  the  subject 
is  at  present  understood.  If  the  views  however  which  we  have 
advanced  be  correct,  these  numbers  certainly  do  not  represent  na- 
ture ;  for  as  we  have  already  stated,  a  strictly  philosophical  arrange- 
ment can  be  rationally  founded  only  upon  the  volumes  of  bodies 
in  the  gaseous  state,  in  which  state  some  common  volume  in  all  in- 
stances should  be  considered  as  the  molecular  unity.  Now,  as 
in  most  instances,  this  molecular  unity  seems  capable  of  subdi- 
vision, of  course  the  number  made  to  represent  it  can  hardly  ever 
be  supposed  to  be  a  prime  number.  Hence,  as  combining  mole- 
cules of  bodies  exist  both  below  and  above  the  molecular  unity, 
they  may  often  (perhaps  always)  be  represented  by  a  series.  Thus 
suppose  9  to  represent  the  molecular  unity  or  volume  of  water, 
and  that  this  be  subdivided  into  three  (which  it  is  at  least,  and 
probably  into  a  much  greater  number)  ;  the  molecular  combina- 
tions of  water  may  be  represented  by  the  series,  3,  6,  9,  12,  15, 
18,  (fee.  We  mean  to  say,  the  molecules  of  water  as  they  actu- 
ally enter  into  a  combination  in  different  bodies,  may  be  supposed 
to  be  represented  by  these  numbers  ;  while,  by  way  of  distin- 
guishing the  different  molecules,  those  below  9,  may  be  desig- 
nated generally  st<6-molecules,  and  those  above  sz</?er-molecules ; 
and  the  molecular  unity  itself  may  be  simply  called  the  molecule^ 
or  in  the  gaseous  state  the  self -repulsive  molecule;  distinctions, 
which  for  the  sake  of  convenience,  we  have  adhered  to  throughout 
these  remarks,  and  which  we  have  thought  it  thus  necessary  to 
explain.* 

Section  III. 

General  Bemarks  upon  Chem^ical  Compounds, 

The  number  of  chemical  compounds  is  so  great  that  an  attempt 
to  enumerate  them  here  would  be  quite  out  of  place  ;  we  shall 
therefore  content  ourselves  with  stating,  as  briefly  as  possible,  the 
general  principles  upon  which  these  compounds  are  formed. 

We  have  already  pointed  out  many  of  the  more  remarkable 
compounds,  when  speaking  of  simple  bodies  ;  and  in  subsequent 
parts  of  this  volume  we  shall  have  occasion  to  allude  to  others.  In 

*  The  above  terms  are  to  be  considered  as  a  temporary  expedient  only. 
If  these  views  be  established  it  will  not  perliaps  be  difficult  to  devise  here- 
after both  a  notation  and  a  nomenclature  founded  upon  them.  At  present 
such  an  attempt  would  be  ridiculous. 


96  CHEMISTRY. 

speaking  of  simple  bodies  we  showed  that  by  far  the  greater  num- 
ber of  ihem  occur  in  the  metallic  state,  and  are  incapable  of  ex- 
istence upon  the  surface  of  our  globe,  on  account  of  the  tendency 
they  possess  to  enter  into  combination,  particularly  with  oxygen. 
It  would  seem  also,  from  the  intensity  of  the  properties  and  the 
general  incompatibility  of  the  simple  bodies  with  the  present  order 
of  things,  tiiat  their  compounds,  rather  than  themselves,  were  the 
objects  the  Autlior  of  nature  had  in  view.  Hence  perhaps  we  are 
more  immediately  interested  in  the  character  of  the  compounds 
than  in  that  of  the  elements  themselves.  Of  the  general  nature 
of  these  compounds,  the  following  observations,  taken  chiefly  from 
Dr.  Thomson's  work  on  chemistry,  will  serve  to  convey  some 
idea  to  the  general  reader. 

The  COMPOUNDS  which  bodies  form  with  one  another  are  either 
PRIMARY  OR  SECONDARY.  By  PRIMARY  COMPOUNDS  are  usually  un- 
derstood tho^^e  which  are  formed  by  the  combination  of  two  or 
more  simple  boilies  with  each  other  ;  while  by  secondary  com- 
pounds are  meant  the  compounds  formed  by  the  union  of  the  pri- 
mary compounds  with  each  other. 

The  PRIMARY  COMPOUNDS  naturally  divide  themselves  into  three 
grand  classes,  viz.  acids,  alkalies  or  bases,  and  neutrals  ;  on  each 
of  which  we  shall  make  a  few  remarks. 

Of  Jicids.  Formerly  it  was  considered  as  requisite  that  bo- 
dies, in  order  to  belong  to  the  class  of  acids,  should  have  a  sour 
taste,  should  be  soluble  in  water,  and  should  have  the  property  of 
reddening  vegetable  blue  colours  ;  and  these  properties  do  indeed 
belong  to  some  of  the  most  common  and  powerful  acids.  But 
there  are  various  acids  which  have  no  taste,  which  are  not  soluble 
in  water,  and  some  which  are  incapable  of  altering  the  colour  of 
the  most  delicate  vegetable  blues  ;  hence  the  term  acid,  as  at  pre- 
sent employed  by  chemists,  is  understood  to  denote  a  substance 
which  has  the  property  of  combining  with,  and  neutralizing,  al- 
kalies or  bases.  The  celebrated  Lavoisier  endeavoured  to  prove 
that  oxygen  constitutes  an  essential  ingredient  of  all  the  acids  ; 
but  later  observations  have  shown  that  not  only  oxygen,  but  the 
analogous  principles,  chlorine,  bromine,  iodine,  and  fluorine,  are 
also  capable  of  forming  acids  by  uniting  with  several  of  the  acidi- 
fiable  bases.  Still  more  recently,  certain  compounds  of  cyanogen, 
(a  primary  compound  of  carbon  and  azote),  of  sulpliur,  of  se- 
lenium, and  of  tellurium  with  the  aciditiable  bases,  have  been 
ranked  among  the  acids ;  so  that  the  acids  at  present  known  may 
be  divided  into  nine  classes,  viz.,  oxygen  acids,  chlorine  acids, 
bromine  acids,  iodine  acids,  Jiuorine  acids,  cyaiiogen  acids,  sul- 
phur acids,  selenium  acids,  and  tellurium  acids. 

Tiie  oxygen  acids  are  more  numerous  and  better  understood 


CHEMICAL  COMPOUNDS.  97 

in  general  than  the  other  classes  ;  they  may  be  subdivided  into 
two  kinds ;  those  with  a  single  base;  and  those  with  a  compound 
base.  The  acids  with  a  single  base  amount  to  between  thirty  and 
forty,  and  include  most  of  the  best  known  and  most  important  of 
those  used  in  chemical  processes  and  in  the  arts  ;  such  as  carbonic 
acid,  sulphuric  acid,  phosphoric  acid,  nitric  acid.  Sic.  The 
oxygen  acids  with  a  compound  base  are  chiefly  derived  from  the 
vegetable  or  animal  kingdoms  ;  they  are  still  more  numerous  than 
those  with  a  single  base,  the  number  at  present  known  amounting 
to  upwards  of  sixty  ;  as  instances  may  be  mentioned  the  tartaric 
acid,  the  citric  acid,  the  malic  acid,  the  lithic  acid,  &c. 

The  chlorine  acids  are  perhaps  as  numerous  as  those  contain- 
ing oxygen,  but  they  have  been  much  less  studied,  and  are,  con- 
sequently, much  less  understood.  One  of  the  most  familiarly 
known  belonging  to  this  class  is  the  muriatic  or  hydrochloric  acid, 
which  is  composed  of  chlorine,  united  with  hydrogen  :  and  here 
may  be  noticed  a  remarkable  circumstance,  that  not  only  chlorine, 
but  all  the  other  allied  principles,  when  they  combine  with  hy- 
drogen, form  powerful  acids  ;  while  the  compound  of  oxygen  with 
hydrogen,  as  we  have  formerly  noticed,  is  ivater,  a  substance  al- 
together dissimilar.  Such  is  the  wonderful  and  inexplicable  na- 
ture of  chemical  combinations  ! 

The  acids  containing  bromine,  iodine,  and  fluorine,  are  still 
less  satisfactorily  known  than  those  containing  chlorine.  As  just 
observed,  the  acids  formed  by  these  different  principles  with  hy- 
drogen, viz.  the  hydrobromic,  the  hydriodic  and  the  hydrofluoric 
acids,  possess  the  most  decided  properties  and  are  best  understood. 

The  cyanogen  acids  are  numerous  and  important,  as  most  of 
them  are  poisonous  ;  thus  the  compound  of  cyanogen  and  hydro- 
gen (analogous  to  those  above  mentioned)  is  the  hydrocyanic,  or 
prussic  acid,  one  of  the  most  virulent  poisons  in  nature,  and  in- 
stantly fatal  to  organic  life  in  every  form. 

Of  the  remaining  acids,  the  sulphur  acids,  the  selenium  acids, 
and  the  tellurium  acids,  we  know  very  little.  Those  with  which 
we  are  at  present  best  acquainted  are  analogous  to  the  preceding 
acids,  and  are  formed  by  the  union  of  the  different  principles  with 
hydrogen.  These  acids  were  formerly  knov\^n  under  the  names 
of  sulphuretted,  seleniated,  and  telluretted  hydrogen;  but  some 
chemists  have  now  given  them  new  names  conformably  to  the 
above  nomenclature. 

Of  alkalies  and  bases.  Bodies  of  this  class,  are,  like  the  acids, 
composed  of  different  elementary  principles,  and  particularly  of 
certain  metals,  combined  with  oxygen,  chlorine,  &c.,  but  usually 
in  less  proportions  than  in  the  acids.  Hence  the  alkaline  bases 
are  as  numerous  as  the  acids,  and  may  be  divided  in  a  simi- 
lar manner  into   oxygen   alkalies,    chlorine  alkalies,    &c.     Of 

9 


98  cHE:\nsTRY. 

these  the  oxygen  alkalies  are  by  far  the  best  known  and  most  im- 
portant, and  they  may,  like  the  oxygen  acids,  be  subdivided  into 
uvo  kinds,  viz.  those  with  a  single  base,  and  those  with  a  com- 
pound base.  The  alkalies  with  a  single  base  include  all  the  well 
known  common  alkaline  bodies,  potash,  soda,  lime,  baryta,  Sic. ; 
while  the  alkalies  with  a  compound  base  are  chiefly  from  the  ve- 
getable kingdom,  and  comprehend  the  newly  discovered  alkaline 
matters,  so  successfully  introduced  into  medicine ;  such  as  quinine, 
from  hd.Yk,  morphine,  from  opium,  &;c.,  the  composition  of  which 
at  present  is  not  well  understood.  »,^mmonia  or  the  volatile  alkali, 
may  perhaps  be  referred  to  this  class  of  alkalies  ;  though  its  com- 
position as  consisting  of  hydrogen  and  azote  only,  without  oxygen, 
may  be  considered  as  constituting  an  exception  or  anomaly. 

The  other  alkaline  bodies  into  which  chlorine,  iodine,  &c., 
enter,  are  very  little  known,  and  some  perhaps  may  be  even  in- 
clined to  doubt  their  existence. 

Of  neutral  compounds.  These  are  arranged  by  Dr.  Thomson, 
under  seven  heads,  the  mere  naming  of  which  will  probably  be 
all  that  is  required,  to  convey  to  the  general  reader  a  sufficient 
notion  of  their  nature.  They  are  water,  spirits  or  alcohol,  ether, 
ethcd,  (a  peculiar  oily  substance  obtained  from  spermaceti)  vola- 
tile oils,  Jixed  oils,  and  bitumens. 

Such  is  a  summary  of  the  primary  cojipounds  and  of  the  prin- 
ciples upon  which  they  have  been  most  recently  arranged.  We 
come  now  to  consider  briefly 

The  SECONDARY  COMPOUNDS,  or  those  formed  by  the  union  of 
the  primary  compounds.  As  the  neutral  primary  compounds  (if 
we  except  water)  enter  into  few  combinations,  it  is  obvious  that 
the  SECONDARY  COMPOUNDS  must  cousist  chiefly  of  substances 
formed  by  the  union  of  the  other  two  general  classes  of  bodies, 
namely,  of  acids  and  alkalies.  These  secondary  compounds 
are  usually  denominated  salts  ;  they  constitute  a  very  numerous 
and  most  important  class  of  bodies  ;  and  as  resulting  from  the 
mutual  union  and  saturation  of  all  the  diflerent  principles  capable 
of  combining  with  each  other,  they  of  course  are  more  abundant 
than  any  other  bodies  ;  indeed,  the  surface  of  our  globe,  may  in 
a  great  measure,  be  considered  as  made  up  of  them.  The  term 
salt  was  originally  confined  to  common  salt ;  but  by  a  singular 
fate,  this  body,  as  being  composed  of  chlorine  and  sodium  only, 
is  now  excluded  from  the  class  of  salts:  saks  being,  as  we  have 
just  said,  considered  by  chemists,  to  be  formed  by  the  union  of 
acids  and  alkalies  only.  As  there  are  nine  classes  of  acids,  of 
course  there  must  be  as  many  classes  of  salts  ;  of  these,  the 
oxygen  acid  salts  are  by  far  the  best  known  and  the  most  im- 
portant; and,  indeed,  this  class  includes  the  greater  number  of 
those  salts  employed  by  chemists  or  in  the  arts.     If  these  salts 


RECAPITULATION.  99 

be  arranged  according  to  their  bases,  which  perhaps  upon  the 
whole,  in  the  present  state  of  our  knowledge,  is  the  best  mode 
of  arranging  them,  they  will  be  found  to  constitute  upwards  of 
fifty  genera;  and  if  we  consider  that  each  of  these  genera  includes, 
in  most  cases,  a  great  number  of  species,  we  may  form  some  idea 
of  the  wonderful  variety  of  bodies  existing  in  nature,  and  with  the 
properties  of  which  the  chemist  is  required  to  be  conversant. 
Familiar  instances  of  the  oxygen  acid  salts  are,  nitre,  common 
chalk,  gypsum  ;  various  metallic  salts,  as  the  white,  green,  and 
blue  vitriols,  &c.  &:c. 

Of  the  chlorine  and  the  other  classes  of  salts  very  little  is 
known,  and  tliis  little  is  chiefly  confined  to  the  salts  composed  of 
these  principles  and  of  hydrogen.  The  hydrochloric  or  muriatic 
acid  combines  with  ammonia,  and  forms  the  well-known  compound 
sal-ammoniac,  a  salt  supposed  to  be  a  true  hycho chlorate  or  mu- 
riate. But  this  is  the  only  instance  known  ;  and  in  all  other 
analogous  instances,  the  hydrogen  of  the  hydrochloric  acid  and 
the  oxygen  of  the  base,  unite  to  form  water,  which  is  separated 
or  separable ;  and  thus  the  chlorine  and  the  metallic  base  are  left 
in  union  by  themselves  in  the  state  of  a  chloride.  This  is  the 
case,  for  instance,  with  common  salt  ^  which,  as  we  before  said, 
is  in  reality  a  chloride  of  sodiitin,  that  is  to  say,  a  simple  com- 
pound of  chlorine  and  the  metal  sodium.  Similar  remarks  ap- 
pear to  be  applicable  to  the  other  analogous  compounds.  It  must 
be  confessed,  however,  that  our  knowledge  with  respect  to  all 
these  matters  is  at  present  in  a  very  unsatisfactory  state,  and  is 
probably  destined  at  no  very  distant  time  to  undergo  a  complete 
revolution. 


Section  IV. 

Recapitulation.     General  Reflections  on  the  Subjects  treated  of 

in  the  preceding  Chapiters. 

The  subjects  considered  in  the  present  chapter  may  be  viewed 
as  a  continuation  of  what  has  engaged  our  attention  in  those  that 
have  preceded  ;  and  the  principal  circumstances  detailed  may  be 
thus  recapitulated. 

1.  All  perfecdy  gaseous  bodies  combine  with  reference  to 
their  volume  ;  that  is  to  say,  any  volume  or  bulk  of  a  gas  always 
combines  with  an  equal  volume  or  bulk  of  the  same  or  of  another 
gas  ;  or  with  a  volume  having  some  simple  relation  to  its  own 
volume,  as  half,  or  twice  as  much  ;  &c.  and  not  with  any  inter- 
vening fractional  part  of  a  volume. 

2.  The  same  volume  of  different  gaseous  bodies  has  very 


100  CHEMISTRY. 

different  ivcights :  hence  on  the  supposition  formerly  advanced, 
that  all  perfectly  gaseous  bodies  under  tlie  same  pressure  and 
temperature  contain  an  equal  number  of  self-repulsive  molecules, 
tlie  molecules  of  different  gaseous  bodies  must  also  have  different 
weights  ;  Avliich  weights  will  be  as  the  specific  gravities  of  the 
gases,  and  may  be  represented  by  numbers  proportional  to  these 
specific  gravities. 

3.  From  the  above  relation  between  the  volumes  and  the 
weights  of  bodies  in  the  gaseous  state,  it  follows,  that  all  bodies 
must  combine  ivith  reference  to  their  weights  ;  that  is  to  say, 
that  the  same  weight  of  the  same  body  (or  half  or  twice  as  much, 
&c.)  must  always  combine  with  the  same  weight  (or  half  or  twice 
as  much,  &;c.)  not  only  of  the  same,  but  of  every  other  body. 

4.  The  numbers  representing  the  relations  among  the  specific 
gi'avilies  of  bodies  in  the  gaseous  state,  are  called  the  molecular 
or  atomic  ivcights  of  the  different  bodies. 

Such  is  the  foundation  of  what  is  usually  called  the  Atomic 
Theory,  the  principles  of  which  are  generally  admitted  as  regu- 
lating chemical  combinations. 

AVe  shall  now  conclude  the  present  Treatise  on  chemistry- 
with  a  {^\N  remarks  more  especially  relating  to  the  object  of  these 
volumes.  And  here  it  may  be  observed,  once  for  all,  that  through- 
out the  preceding  pages,  as  well  as  in  what  follows,  we  have 
endeavoured  to  state  each  argument  as  distinctly  as  possible, 
without  encumbering  it  too  much  with  details — in  short,  to  illus- 
trate principles  rather  than  to  enumerate  particulars.  When  the 
principles  of  a  cumulative  argument  are  understood,  the  details 
are  readily  supplied  by  the  reader. 

First.  On  taking  a  general  and  collective  review  of  the  facts 
brought  forward  in  the  preceding  chapters,  the  circumstances 
calculated  to  strike  our  attention  in  the  first  place,  are  the  won- 
derful coincidence  between  the  priority  of  existence,  and  the  uni- 
versal prevalence  of  the  primordial  agents  and  elements  of  nature, 
on  the  one  hand ;  and  on  the  other,  the  beautiful  adaptation  of 
the  agents  and  elements  of  a  later  and  more  subordinate  character 
to  these  primordial  principles  ;  so  that  when  the  whole  are  taken 
together  they  constitute  one  harmonious  and  connected  series, 
in  which  all  the  various  parts  are  mutually  adapted  and  dependent. 
In  the  following  chapters  we  shall  have  occasion  to  notice  many 
of  the  more  important  of  these  subordinate  arrangements ;  at 
present  we  shall  chiefly  confine  ourselves  to  a  general  review  of 
what  has  been  already  stated. 

We  are  told  by  the  inspired  historian  that  after  matter  had  been 
created  and  endowed  with  motion,  the  next  Almighty  fiat  was 
"let  there  be  light;"  and  if  we  suppose  this  fiat,  to  have  in- 
cluded the  other  imponderable  forms  of  matter,  heat,  &c.,  how 


GENERAL  ARGUMENTS.  101 

entirely  do  the  whole  phenomena  of  nature  accord  with  the  sacred 
narrative  ?  Light,  and  probably  its  attendant  heat,  are  the  most 
generally  diffused  and  universal  of  all  the  subordinate  agencies  ; 
so  much  so,  that  they  are  not  confined  to  our  globe  or  even  sys- 
tem, but  extend  throughout  the  universe.  Their  laws  and  influ- 
ences, therefore,  seem  to  be  as  general  and  as  necessary  to  the 
present  order  of  things,  as  those  of  gravitation  itself.  The  prior- 
ity of  existence  also  of  light  and  of  heat  is  self-evident ;  for  until 
they  existed,  nothing  else,  as  we  are  acquainted  with  things, 
could  have  had  existence.  Now  all  subsequent  creations  have 
been  made  with  the  most  exact  regard  to  the  influences  of  these 
prior  agencies.  The  globe,  for  example,  which  we  inhabit,  is  at 
a  certain  distance  from  the  sun,  the  great  centre  of  our  system 
and  of  light  and  of  heat ;  and  where  of  course,  according  to  the 
laws  which  light  and  heat  obey,  they  must  act  with  a  certain  in- 
tensity. Hence  it  was  necessary  that  the  materials  of  this  globe 
should  have  a  certain  degree  of  fixity,  otherwise  they  could  not 
exist.  If  indeed  there  had  been  no  ulterior  views,  with  respect 
to  the  destination  of  this  globe  ;  all  that  would  have  been  requi* 
site,  would  have  been  to  have  made  it  sufiiciently  firm  to  move 
through  space  ;  and  for  this  purpose  the  more  homogeneous  and 
compact  its  composition  had  been  the  better.  But  what  are  the 
facts  ?  Our  globe,  though  stable,  so  far  from  being  homogeneous, 
is  composed  of  a  variety  of  substances  all  differing  from  each 
other  in  their  properties  ;  some  being  solid,  some  fluid,  some 
aeriform  under  the  common  circumstances  in  which  they  have 
been  placed,  and  all  beautifully  adapted,  both  by  their  physical 
and  chemical  properties,  to  the  purposes  they  fulfil  in  nature  ; 
and  what  is  more,  to  the  purposes  they  were  designed  to  fulfil  in 
nature  ;  for  on  no  other  supposition  would  their  properties  be  in- 
telligible. 

Thus  water,  ivithin  very  narroiv  limits  of  temperature,  is  a 
solid,  or  a  liquid,  or  a  gas ;  and  yet  these  very  narrow  limits  of 
temperature,  neither  more  nor  less,  are  precisely  those  which  ex- 
ist upon  the  surface  of  our  globe ;  where  they  are  the  natural  and 
necessary  results  of  its  situation  in  the  universe,  and  of  the  general 
laws  which  govern  the  distribution  of  light  and  heat.  Had  the 
properties  of  this  body  been  other  than  what  they  are,  or  had  the 
general  temperature  of  our  globe  been  different,  water  would  have 
existed  altogether  in  the  solid  or  in  the  gaseous  state,  and  its  most 
important  properties  would  have  been  unknown.  Hence  it  seems 
almost  impossible  to  arrive  at  any  other  conclusion,  than  that  the 
temperature  of  the  earth,  and  the  properties  of  the  water  on  its 
surface,  have  been  mutually  adjusted  to  each  other.  And  further, 
since  the  temperature  of  the  earth,  as  just  stated,  is  the  natural  re- 
sult of  the  general  laws  which  govern  the  distribution  of  heat  and 
of  light ;  the  inference  must  be,  that  the  properties  of  the  water, 

9* 


102  CHEMISTRY. 

as  the  subordinate  and  later  principle,  have,  at  an  after  period,  been 
adjusted  to  the  prior  temperature  of  the  earth. 

If  we  do  not  admit  of  this  adjustment,  we  must  suppose  that 
the  whole  has  been  the  result  of  chance,  or  of  some  other  unin- 
telligent principle ;  and  if  water  had  been  the  only  principle  in 
which  such  adaptations  were  apparent,  the  supposition  of  chance 
might,  perhaps,  be  received  ;  at  least  it  would  have  been  difficult 
to  prove  the  contrary.  But  when  we  see  similar  happy  adjust- 
ments in  every  object  around  us, — in  the  different  elements  of  the 
air  we  breathe,  the  soil  we  tread  upon,  the  rocks  in  all  their  va- 
rieties, composing  the  solid  crust  of  our  globe,  not  one  of  which 
could  have  been  more  happily  contrived  for  the  purposes  they  ful- 
fil, nor  indeed  be  scarcely  conceived  to  exist  otherwise  than  what 
they  are,  without  destruction  to  the  whole  of  the  present  arrange- 
ments— when  we  see  all  these  things,  and  duly  reflect  upon  them, 
it  becomes  absolutely  impossible  to  admit  that  so  much  happy 
adjustment,  so  much  apparent  intelligence,  so  much,  in  short,  of 
what  the  veriest  sceptic  under  other  circumstances  would  have 
allowed  to  have  been  evidences  of  design,  can  be  evidences  of  any 
thing  else  than  design,  or  have  resulted  from  any  unintelligent  cause 
whatever.  Hence  we  are  driven  irresistibly  to  the  only  rational 
conclusions  which  the  premises  appear  to  admit  of,  viz.,  that  all 
these  happy  adjustments  and  adaptations  which  we  see  in  nature, 
are  really  and  truly  what  they  appear  to  be, — so  many  evidences 
of  design  ;  and,  consequently,  that  the  whole  have  sprung  from 
the  will  of  an  intelligent  and  omnipotent  Creator. 

The  above  inferences  are  deducible  from  the  plain  and  obvious 
arrangements  of  nature,  which  every  one  can  readily  understand : 
but  when  speaking  of  elementary  bodies  we  remarked,  that  in  a 
variety  of  instances,  their  object  and  use  were  unknown  to  us ; 
and  before  we  quit  this  part  of  the  subject,  it  may  not  be  out  of 
place  to  consider  briefly  these  difficult  points. 

When  we  see  adjustments  so  wonderful,  and  such  wisdom  dis- 
played in  those  parts  of  creation  which  are  intelligible  to  us,  we 
cannot  imagine  that  the  Being  who  made  them  all  would  act  other- 
wise than  with  wisdom.  Hence  what  we  do  not  understand,  or 
what  may  appear  incongruous  to  us,  we  naturally  and  properly 
refer  to  our  own  ignorance.  The  phenomena  of  chemistry  are  so 
extraordinary  and  often  so  unexpected,  that  little  in  general  can 
be  predicated  of  them,  beyond  what  is  actually  known.  The 
most  experienced  chemist,  therefore,  as  compared  with  the  Great 
Chemist  of  nature,  is  immeasurably  deficient;  and  can  only  con- 
template His  wonderful  operations  with  astonishment  and  awe, 
and  own  them  unapproacliable.  Who  then  can  tell  what  design 
is  latent  under  apparent  incongruities  ?  What  elaborate  contri- 
vances and  adaptations  may  have  been  requisite  to  have  produced 


GENERAL  ARGUMENTS.  103 

water  or  carbon,  or  any  other  essential  principle,  out  of  the  mate- 
rials and  in  conformity  to  the  laws,  by  means  of  which  the  Great 
Author  of  nature  chose  to  operate  ?  Who  can  tell  that  the  minor 
evil  may  not  have  been  essential  to  the  existence  of  the  greater 
good  ?  That  the  poisonous  metals,  for  instance,  are  not,  as  it 
were,  the  refuse  of  the  great  chemical  processes  by  which  the  more 
important  and  essential  principles  of  nature  have  been  eliminated? 
That  these  poisonous  principles  have  not  been  left  with  such  sub- 
dued properties  as  scarcely  to  interfere  with  His  great  design, — 
not  because  they  could  not  have  been  prevented — not  because  they 
could  not  have  been  removed — but  on  purpose  and  designedly  to 
display  His  power  ? 

Secondly.  If  we  pursue  the  subject  a  step  further,  and  inquire 
into  the  means  by  which  all  the  beautiful  adaptations  we  have 
been  considering  are  effected,  we  shall  find  that  they  principally 
depend  upon  a  certain  due  adjustment  to  each  other  of  the  quali- 
ties and  quantities  of  the  difTerent  substances,  and  more  especi- 
ally of  the  different  elementary  principles,  of  which  our  globe  is 
composed.  These  adjustments  are  so  universal  and  so  varied  in 
their  character,  that  to  enumerate  them  all,  would  be  litUe  else 
than  to  enumerate  all  the  objects  in  nature;  we  shall  therefore 
content  ourselves  with  a  few  of  the  most  familiar  of  each  kind. 

In  the  first  place,  with  respect  to  the  adjustment  of  quality. 
Let  us  consider  for  a  moment  and  by  way  of  illustration,  what 
would  happen  if  the  qualities  of  water  or  of  air  were  to  undergo 
a  change :  were,  for  example,  the  important  fluid  water  to  become 
sour  or  sweet,  or  heavier  or  lighter,  or  indeed  anything  but  what 
it  is ;  or  were  the  air  of  the  atmosphere  to  acquire  odour  or 
colour,  or  to  become  opaque  :  by  either  of  such  changes,  slight 
as  they  appear,  the  whole  of  the  present  economy  of  nature  would 
be  deranged.  Again,  if  the  qualities  of  the  acid  existing  in  the 
common  salt  of  the  ocean  were  to  become  so  modified  as  to  quit 
the  alkali  with  which  it  is  at  present  associated,  and  to  combine 
with  the  limestone  composing  our  rocks  ;  while  the  carbonic  acid, 
thus  set  free,  v/as  diffused  through  the  atmosphere  :  in  such  a 
case  a  large  part  of  the  solid  crust  of  our  globe  would  rapidly 
disappear  and  become  dissolved  in  the  waters  of  the  ocean,  which 
would  thus  be  totally  unfitted  for  their  present  purposes  ;  while 
the  liberated  carbonic  acid  would  instantly  prove  fatal  to  animal 
life.  Such  would  be  the  consequences  of  these  trifling  changes 
in  the  qualities  of  a  few  substances  only  ;  nor  is  it  possible  scarcely 
to  conceive  any  other  change  that  would  not  be  attended  with 
similar  results. 

In  the  next  place,  the  importance  of  the  adjustments  o{  quan- 
tity is  equally  striking.  Let  us,  for  instance,  conceive  what 
would  happen  from  the  simple  inversion  of  the  quantities  of  dry 


104  CHEMISTRY. 

land  and  of  sea  as  they  now  exist:  in  such  a  case  there  would 
not  be  enough  of  water  to  preserve  the  surface  of  the  land  in  a 
moist  state,  and  the  greater  part  would  be  in  the  situation  of  the 
deserts  of  Africa,  and  totally  unfit  for  the  habitation  of  organized 
beings.  When  speaking  of  the  elements  of  water,  we  alluded  to 
the  happy  adjustment  of  the  quantities  of  oxygen  and  hydrogen 
in  the  world  ;  and  to  the  consequences  that  would  have  ensued 
if  hydrogen,  instead  of  oxygen,  had  predominated.  The  same 
remarks  apply  to  almost  every  other  element ;  for  example,  had 
the  proportions  of  chlorine,  and  of  the  soda  in  common  salt ;  or 
of  the  carbonic  acid,  and  of  the  lime  in  our  marbles,  been  anything 
but  what  they  are,  the  one  or  the  other  of  the  ingredients  must 
have  been  in  excess,  and  the  present  order  of  things  could  never 
have  existed.  Again,  were  gold  suddenly  to  become  as  abundant 
as  iron,  and  iron  as  rare  as  gold;  were  the  carbon  existing  in  the 
present  useful  form  of  fossil  coals,  to  assume  the  crystallized  form 
and  become  diamonds  ;  the  whole  order  of  nature  would  be  sub- 
verted, and  the  whole  of  the  present  arrangements  be  involved  in 
ruin.  Those  who  deny  the  argument  of  design,  of  course,  con- 
sider such  suppositions  as  these  absurd  ;  and  if  carried  too  far, 
they  doubtless,  under  any  circumstances,  lose  much  of  their  effect; 
but  admitting  the  argument  of  design,  the  judicious  application  of 
such  suppositions  is  well  calculated  to  place  the  advantages  and 
effects  of  certain  arrangements  in  a  more  striking  point  of  view 
than  can  be  obtained  by  any  other  means.  More  especially,  such 
suppositions,  by  showing  the  wonderful  adaptations  of  subsequent 
creations  to  prior  existences,  are  admirably  calculated  to  illustrate 
the  fitness,  and  consequently  the  apparent  design  displayed  in 
the  formation  of  these  prior  existences  ;  and  thus  to  show  that 
they  must  have  been  created  with  reference  to  ulterior  purposes. 

The  argument  of  prior  arrangements  and  the  subsequent  adap- 
tation to  these  arrangements  of  other  creations  is  one  of  such  in- 
terest, and  its  consequences  are  so  important,  that  perhaps  it  may 
not  be  deemed  irrelevant  if,  for  further  illustration,  we  recapitulate 
the  principal  points  in  a  condensed  form.  For  this  purpose  we 
shall  select  the  obvious  and  familiar  relation  between  water  and 
air,  and  plants  and  animals. 

The  prior  existence  of  water  and  air  as  compared  with  that  of 
plants  and  animals,  is  established  by  the  fact,  that  water  and  air 
can  exist  without  plants  and  animals,  but  that  plants  and  animals 
cannot  exist  without  water  and  air.  Hence  as  water  and  air 
must  have  existed  with  all  their  present  properties  before  plants 
and  animals  were  created,  tlie  question  naturally  arises,  how 
water  and  air  came  to  be  endowed  with  their  present  properties  ? 
We  suppose  that  water  and  air  were  created  with  their  present 
properties,  with  reference  to  the  future  existence  of  plants  and 


GENERAL  ARGUMENTS.  105 

animals ;  and  on  this  supposilion  the  whole  becomes  intelligible. 
Further,  that  this  is  the  true  explanation,  and  that  water  and  air 
have  not  obtained  their  present  properties  by  chance  or  accident 
is  rendered  still  more  probable  by  the  following  considerations. 
We  have  said  that  water  and  air  can  exist  without  plants  and 
animals  ;  now  as  far  as  we  know,  water  and  air  might  have  ex- 
istedybr  ever  without  plants  and  animals  ;  at  least  the  contrary 
cannot  be  proved  or  even  rendered  probable.  Moreover,  plants 
and  animals,  as  involving  new  principles  of  a  higher  order  (those 
of  life),  never  could  by  any  law  of  nature,  necessary  or  proba- 
ble, have  resulted  from  an  inferior  agency.  Hence  there  is  no 
necessary  relation  of  cause  and  effect  between  the  prior  ex- 
istence of  water  and  air,  and  the  subsequent  existence  of  plants 
and  animals  ;  as  some  seem  to  have  supposed.  Hence  too  it 
follows  irresistibly,  that  plants  and  animals  have  been  created, 
and  their  properties  adapted  to  tiiose  of  water  and  of  air  at  some 
subsequent  period,  and  by  some  external  and  superior  agent. 
But  the  agent  that  could  thus  create  plants  and  animals,  could 
surely  have  created  the  water  and  air  likewise ;  nay,  must  have 
done  so  ;  for,  as  the  prior  and  subsequent  creations  taken  together, 
evidently  form  but  different  parts  of  one  and  the  same  general 
design,  the  whole  design  must  have  been  the  work  of  one  and 
the  same  intelligent  Agent. 

It  yet  remains  to  draw  the  attention  of  the  reader  to  another 
circumstance  connected  with  these  adjustments  in  quality  and 
quantity,  viz.  the  double  adjustment.  Of  the  causes  of  the  qualities 
of  bodies  we  know  but  little,  and  that  little  is  founded  solely  on 
experience.  We  see  that  these  qualities  are  admirably  fitted  for 
their  apparent  purposes,  and  hence  (as  they  might  have  been  dif- 
ferent), we  arrive  at  the  probable  conclusion  that  they  have  been 
so  fitted  by  design.  The  collocation  of  quantities  and  numbers, 
exacdy  where  they  have  been  required,  adds  much  to  the  proba- 
bility of  this  conclusion ;  as  such  a  collocation  could  hardly 
have  been  other  than  the  act  of  an  intelligent  Being.  But  the 
double  adjustment  in  qucdity  and  quantity  of  the  same  thing  at 
the  same  time,  adds  almost  infinitely  to  the  weight  of  evidence  ; 
and  indeed  furnishes  a  proof  in  favour  of  design  and  of  its  conse- 
quences, which  amounts  to  all  but  actual  demonstration. 

Thirdly.  There  is  another  point  of  view  in  which  we  may 
consider  what  has  been  stated,  and  by  which  we  shall  at  the  same 
time  be  brought  a  step  nearer  to  the  existing  order  of  things. 
Amidst  all  that  endless  diversity  of  property,  and  all  the  changes 
constantly  going  on  in  the  world  around  us,  we  cannot  avoid  being 
struck  with  tiie  general  tendency  of  the  whole  to  a  state  of  repose 
or  equilibrium.  Moreover,  this  tendency  to  equilibrium  is  not 
confined  to  the  ponderable  elements,  but  prevails  also  in  the  same 


lOG  CHEMISTRY. 

Striking  degree  among  the  imponderable  agencies,  heat  and  hght; 
which  as  we  have  seen,  cannot  be  any  where  h^ng  retained  in  a 
state  of  excess,  on  account  of  their  natural  disposition  to  acquire 
a  certain  state  of  equilibrium ;  depending  generally  upon  the  place 
of  the  earth  in  the  solar  system.  Now,  tlie  formation  of  this  state 
of  equilibrium,  and  its  preservation,  may  be  considered  as  the 
results  of  those  wonderful  adjustments  among  the  qualities  and 
quantities  of  bodies  above  alluded  to — the  qualities  being  such  as 
to  neutralize  each  other's  activity,  while  the  quantities  are  so 
apportioned  as  to  leave  one  or  two  only  predominant. 

The  preceding  is  a  general  view  of  the  subject.  But  it  is  to 
be  observed,  that  the  state  of  equilibrium  here  described  is  not 
absoluteh^^^cef/;  as  such  an  unyielding  condition  would  be  not 
less  incompatible  with  the  present  order  of  things  than  a  condi- 
tion of  unlimited  change.  The  whole  are  so  adjusted  therefore, 
that  slight  deviations,  or  oscillations  about  the  neutral  point  of 
rest  or  equilibrium,  take  place,  and  are  even  necessary,  as  the 
world  is  at  present  constituted;  though  these  changes  are  bound- 
ed within  very  narrow  limits,  and  greater  deviations  would  in- 
stantly prove  fatal  to  the  whole.  If  we  inquire  into  the  principles 
upon  which  these  slight  deviations  take  place  and  are  regulated, 
we  shall  find  still  further  reason  to  admire  the  wonderful  arrange- 
ments displayed.  When  speakino^  of  the  elements  of  water,  we 
observed  how  much  the  stability  of  nature  depended  upon  the 
proportions  of  the  elements  of  this  fluid;  and  that  one  of  its  ele- 
ments, oxygen,  existed  in  excess,  and  in  a  free  state,  in  the  air. 
Now,  it  is  to  the  agency  of  this  oxygen  in  a  free  state,  and  to'. the 
annual  and  diurnal  motions  of  the  earth,  tliat  most  of  the  minor 
operations  going  on  around  us  are  to  be  referred.  The  universal 
presence  and  peculiar  properties  of  oxygen  are  such  as  to  inter- 
fere more  or  less  with  everything;  while  the  motions  of  the  earth 
keep  everything  in  a  constant  state  of  activity  and  change.  Yet, 
the  general  tendency  of  the  whole,  as  before  observed,  is  towards 
a  state  of  equilibrium;  and  the  principles  upon  which  this  ten- 
dency operates,  are  very  intelligible.  Thus,  all  bodies  below  the 
neutral  point  of  rest,  if  we  may  be  allowed  the  expression  ;  that 
is  to  say,  all  bodies  of  a  marked  elementary  character,  have  a  ten- 
dency to  combine  with  each  other  sxjntheticalhj ;  while  beyond 
the  neutral  point,  bodies  have  very  little  tendency  to  combine 
further ;  and  if  by  intention  on  the  part  of  the  operator,  or  from 
any  other  cause,  they  be  so  made  to  combine,  when  left  to  their 
own  operations,  they  speedily  revert  or  oscillate  back  to  the  point 
of  equilibrium. 

Such  are  the  means  by  which  the  state  of  equilibrium  we  are 
considering  has  been  produced,  and  by  which  it  is  still  preserved; 
nor  is  it  possible  to  reflect  upon  the  subject  for  a  moment  with* 


GENERAL  ARGUMENTS.  107 

out  arriving  at  the  conclusion,  that  this  state  of  equilibrium  pos- 
sesses all  the  characters  of  a  prior  arrangement,  to  which  organized 
beings  have  been  subsequently  adapted.  We  are  thus  led,  in  the 
next  place,  to  make  a  few  remarks  upon  the  subsequent  adaptation 
of  organized  beings  to  the  pre-estabhshed  equilibrium  of  nature. 

Tlie  present  races  of  organized  beings  in  all  instances  are  pro- 
duced only  by  the  process  of  generation;  and  jf  they  were  anni- 
hilated, there  are  no  natural  operations  going  on  in  the  world, 
which  can  lead  us  to  believe,  that  by  any  law  of  Piature  such 
organized  beings  could  be  reproduced.     That  is  to  say,  we  cannot 
conceive  that  hydrogen,  carbon,  oxygen,  and  azote,  with  heat  and 
light,  (fcc.  from  what  we  know  of  their  properties,  would  ever  be 
able,  of  their  own  accord,  so  to  combine  as  to  form  a  plant  or  an 
animal.     Hence,  when  plants  and  animals  were  first  produced,  it 
is  evident  that  there  must  have  been  a  power  or  agent  in  operation, 
which  has  long  since  discontinued  so  to  operate ;   and  that  this 
power  or  agent  not  only  created  plants  and  animals ;  but  at  the 
same  time  imparted  to  them  a  capability  of  perpetuating  their  ex- 
istence, for  a  period,  at  least,  commensurate  with  that  state  of 
equilibrium  in  which  they  have  been  placed.     Now,  whether  we 
consider  the  power  or  agent  who  accomplished  all  these  things, 
to  have  been  the  Deity  himself  operating  immediately,  which  is 
most  probable ;  or  whether  we  consider  with  some,  that  He  ope- 
rated by  delegated  agencies  and  laws,  the  result  is  the  same  as  far 
as  our  argument  is  concerned  ;  the  object  of  which  argument  is 
to  show,  that  the  present  races  of  organized  beings  are  somehow 
or  other  influenced  by  the  same  general  laws  which  appear  to 
regulate  inorganic  matters.     That  is  to  say,  organized  beings  at 
the  present  time,  are  at  least  as  fixed  and  permanent  in  their 
nature,  as  the  state  of  equilibrium  in  which  they  have  been  placed  ; 
and  consequently,  no  new  plants  or  new  animals  can,  as  the  world 
now  exists,  be  imagined  to  be  produced  without  a  new  and  spe- 
cific act  of  creation ;  or  at  least,  without  an  entire  change  in  the 
standard  of  equilibrium. 

We  have  alluded  to  the  commencement  of  the  present  order  of 
things,  and  to  a  possible  state  of  change  in  the  condition  of  equi- 
librium :  perhaps  it  may  not  be  amiss  to  make  a  few  further  re- 
marks upon  these  points.  That  the  present  order  of  things  most 
certainly  has  had  a  beginning ;  and  as  certainly  will  come  to  an 
end,  we  cannot  doubt ;  the  questions  are,  when  was  this  begin- 
ning ;  when  will  be  this  end  ?  Of  the  end  of  course  we  can  know 
nothing  :  the  beginning  is  less  obscure  ;  and  there  are  indelible 
impressions  left  upon  the  materials  and  structure  of  our  globe, 
which  throw  no  ordinary  light  upon  this  question.  The  consi- 
deration of  the  changes  which  our  earth  has  undergone,  however, 
belongs  to  another  department :  we  shall  only  observe  that  these 


108  CHEMISTRY.  ^ 

changes  appear  to  be  of  two  distinct  orders,  which  have  alternated 
with  one  another  in  succession.  The  first  of  these  orders  of 
changes  seems  to  have  been  of  a  slow  and  gradual  kind,  and  such 
as  might  be  supposed  to  take  place  during  a  state  of  things,  more 
or  less  like  the  present,  and  existing  for  a  considerable  period. 
The  changes  of  the  second  order,  on  the  contrary,  have  evidently 
been  violent,  sudden,  and  disruptive,  of  comparatively  short  dura- 
tion, and  differing  exceedingly  in  degree  and  in  extent.  In  general 
they  appear  to  have  operated  from  within  ;  but  whether  altogether 
from  internal  or  from  external  influences,  is  unknown  to  us.  Now, 
it  is  remarkable  that  these  successive  alternations  seem  each  time 
to  have  changed  the  standard  of  equilibrium  ;  and  that  during  the 
state  of  comparative  quietude,  or  the  interval  of  equilibrium  be- 
tween the  convulsions,  organized  beings  have  existed,  adapted  to 
the  exigencies  of  that  particular  state  of  equilibrium  ;  and  which 
beings  must  have  been  successively  created  :  moreover,  the  later 
creations  gradually  approach  to  those  at  present  in  existence. 
Hence,  the  change  in  the  standard  of  organization  seems  to  have 
been  not  only  simultaneous  with  the  change  in  the  state  of  equi- 
librium ;  but  doth  appear  to  have  been  progressively  raised  after 
each  convulsion.  Finally,  tiie  last  general  catastrophe  of  the  dis- 
ruptive order  was  evidently  a  deluge.*  Such  are  the  conclusions 
which  geologists  have  deduced  from  a  careful  survey  of  that  part 
of  the  crust  of  the  earth  to  which  they  have  access;  and  these 
conclusions  are  of  the  most  important  kind.  In  particular,  by 
demonstrating  the  existence  of  successive  adaptations  to  different 
successive  states  of  equilibrium,  they  place  the  argument  of  design 
in  a  new  light,  and  add  in  no  small  degree  to  its  force.  This 
part  of  the  subject,  however,  belongs  to  the  geologist,  to  whom, 
for  the  present,  we  shall  leave  it. 

Fourthly.  The  argument  of  design  as  connected  with  the 
subject  of  equilibrium  above  treated  of,  may  be  considered  yet 
in  another  point  of  view.  In  this  state  of  equilibrium  we  have 
observed  that  the  properties  of  bodies,  as  they  actually  exist  around 

•  If  we  juclg'e  from  what  we  see  going  on  in  nature  around  us,  and  from 
the  little  tendency  there  appears  to  be  in  tiling's  at  present  to  combine 
into  new  forms,  we  must  be  almost  led  to  the  conclusion  that  the  deve- 
lopement  of  new  elements,  as  well  as  of  new  agents,  is  necessary  to  pro- 
duce new  and  specific  arrangements.  May  we  not  then  infer  that  during 
those  periodic  convulsions  alluded  to  in  tbe  text,  new  elements  have  been 
developed,  or  old  ones  decomposed  into  others  of  a  higher  and  more  ele- 
mentary kind;  and  that  in  virtue  of  the  general  laws  in  operation,  these 
new  elements  have  subsequently  combined  to  form  series  of  new  arrange- 
ments ?  Of  course  this  supposition  is  intended  to  apply  only  to  the  means 
adopted  by  the  Deity  to  ellect  his  purpose.  The  formation  and  selection 
of  these  new  elements  must  in  all  instances  be  supposed  to  result  Immedi- 
ately from  his  will  and  agency. 


GENERAL  ARGUMENTS.  109 

US,  are  all  so  subdued  and  passive  in  their  character,  that  no  one 
predominates  over,  or  excludes  the  other.  Now,  when  we  re- 
flect that  almost  all  these  bodies  are  compounds,  and  when  we 
compare  the  properties  of  these  compounds  with  the  properties 
of  the  elements  composing  them,  it  is  impossible  not  to  infer,  that 
the  properties  of  the  compounds  rather  than  those  of  the  elements, 
were,  at  their  origin,  the  objects  contemplated.  That  is  to  say; 
in  order  that  the  compounds  might  be  perfect,  the  elements  cal- 
culated to  produce  them,  were  created  essentially  such  as  these 
compounds  might  require,  without  reference  to  the  secondary  pro- 
perties of  the  elements  tiiemselves  ;  which  were  left  to  be  deter- 
mined as  the  more  general  laws  of  matter  might  decide.  For  in- 
stance, the  properties  of  hydrogen  in  water,  and  of  chlorine  and 
sodium  in  common  salt,  not  being  required  in  the  economy  of 
nature,  the  properties  of  these  elements  have  not  been  made  com- 
patible with  organic  existence  ;  and  the  whole  attention  (if  such 
a  terra  may  be  applied  to  the  operations  of  the  Deity)  has  been 
directed  to  the  properties  of  the  compounds,  water  and  salt.  Thus, 
on  the  one  hand,  where  required,  we  have  the  most  striking  adap- 
tation of  property;  while  on  the  other,  where  not  required,  this 
adaptation  of  property  has  not  been  attended  to  :  nor  is  this  true 
of  water  and  salt  only,  but  of  almost  every  other  compound  in 
nature.  Nay,  what  is  more,  the  incongruities  of  the  whole  sys- 
tem have,  with  the  most  consummate  skill,  been  thrown,  as  it 
were,  among  those  properties  not  required.  Hence,  the  arrange- 
ments of  nature  viewed  in  this  light,  not  only  exhibit  novel  evi- 
dences, but  some  of  the  most  slrikina:  evidences  of  design  that  we 
possess. 

The  subject  of  the  mcongruous  properties  of  bodies  is  one  of 
great  interest.  We  have  seen  that  many  of  the  elementary  prin- 
ciples are  poisonous  ;  and  that  almost  all  of  them,  if  liberated  from 
their  affinities,  and  sent  abroad  in  the  world,  like  so  many  demons 
let  loose,  would  instantly  bring  destruction  upon  the  whole  fabric. 
Now,  why  should  such  incompatible  properties  be  necessary  to 
the  properties  of  the  compounds?  Why,  tor  instance,  should  the 
incombustible  fluid  water  contain  one  of  the  most  combustible 
principles  in  nature  ?  or  the  mild  and  innocuous  common  salt  be 
composed  of  two  elements,  which,  in  their  separate  state,  would 
instantly  destroy  life  ?  Why,  do  we  repeat,  are  these  deleterious 
properties  of  the  elements  necessary  to  the  wholesome  condition 
of  tlie  compound  ?  What  part  do  they  perform  ;  or  what  property 
do  they  contribute  to,  or  represent  ?  These  are  questions  utterly 
beyond  our  comprehension,  and  are  likely  always  to  remain  so. 
That  these  incompatible  properties  of  the  elements,  however,  do, 
in  some  way,  contribute  to  the  perfection  of  the  compounds,  we 
cannot  doubt ;  and  the  only  grounds  upon  which  such  incompati- 

10 


110  CHEMISTRY. 

bilily  seems  to  admit  of  explanation  is,  that  it  results  necessarily 
from  those  limitations  which  the  Deity  has  thouirht  proper  to  pre- 
scribe to  his  power,  and  to  which  he  always  most  rigidly  adheres. 
iMoreover,  be  the  reason  what  it  may,  it  is  evident  that  these  ar- 
rangements, so  immediately  calculated  to  lead  to  practical  difficul- 
ties, have  been  the  result  of  choice.  For  we  cannot  but  believe 
that  an  omnipotent  Creator,  if  he  had  so  willed,  could  have  made 
the  elements  innocuous,  as  well  as  the  compounds  ;  nay,  to  our 
limited  understanding  this  would  have  been  the  easiest  and  most 
natural  mode  of  proceeding.  Why  then  did  he  choose  the  appa- 
rently more  difficult  course  ?  Why,  to  use  the  language  of  Paley, 
but  "  that  he  might  let  in  and  thereby  exhibit  demonstrations  of 
his  wisdom."  Throuirhout  nature,  the  exigencies  and  incongrui- 
ties  necessarily  arising  from  the  arrangements  we  have  been  con- 
sideringf,  have  given  occasion  for  the  display  of  the  most  astonish- 
ing wisdom  and  power.  And  instead  of  that  jarring  and  clashing 
which  might  have  been  expected  froin  so  many  conflicting  ele- 
ments, the  qualities  and  quantities  of  these  elements  have,  upon 
the  whole,  been  so  wonderfully  adjusted  to  each  other,  that  they 
neutralize  and  balance  each  other's  evils  ;  and  the  general  result 
has  been,  that  all  have  finally  settled  down  together  into  that  har- 
monious state  of  equilibrium  before  alluded  to,  so  admirably  adapt- 
ed for  the  existence  of  organic  life. 

Fiftlily.  We  have  hitherto  confined  our  attention  to  general 
principles  and  arrangements  ;  but  the  commonest  chemical  pro- 
cess may  be  made  to  furnish  us  with  some  striking  proof  of  the 
omnipotence  of  the  great  Creator.  Let  us  for  example  consider 
what  happens  in  a  simple  and  familiar  instance  of  chemical  de- 
composition ;  as  when  a  solution  of  lunar  caustic  (nitrate  of  silver) 
is  added  to  a  solution  of  common  salt.  In  this  case,  the  chlorine 
of  the  salt  combines  with  the  silver,  and  produces  a  curdy  pre- 
cipitate which  falls  to  the  bottom  ;  while  the  nitric  acid  combines 
with  the  soda,  and  forms  a  soluble  salt  which  remains  in  solution. 
Now,  we  showed  in  a  former  chapter  that  the  minutest  fragment 
of  matter  appreciable  by  our  senses,  consists  of  innumerable  mole- 
cules. If  therefore  we  suppose  a  small  quantity,  as  an  ounce,  of 
the  lunar  caustic,  and  a  proportionate  quantity  of  common  salt,  to 
be  mixed  together  ;  what  countless  myriads  of  molecules,  in  a 
portion  of  time  literally  inappreciable,  must  have  sought  out,  and 
combined  each  with  its  fellow,  in  this  simple  process  !  The  hu- 
man mind  absolutely  recoils  from  the  contemplation  of  objects  so 
completely  beyond  its  powers  ;  for  the  utmost  that  we  can  imagine, 
must  fall  almost  infinitely  short  of  the  reality.  Were  we,  for  il- 
lustration, to  conceive  every  human  being  at  present  in  existence, 
to  be  collected  tofrcther  into  one  vast  array,  and  to  be  all  dressed 
exactly  alike,  and  to  perform  the  same  military  manteuvre  at  the 


OBJECTIONS  TO  DESIGN.  Ill 

same  moment ;  we  should  be  probably  as  far  short  of  the  actual 
numbers  of  similar  molecules,  each  manoeuvring  exactly  alike  in 
the  above  simple  experiment,  as  a  single  company  falls  short  of 
our  congregated  army  !  Again,  to  take  another  familiar  illustration, 
as  the  working  of  a  common  steam  engine;  we  are  assured  that 
in  this  simple  operation,  there  are  more  self-repulsive  molecules 
of  water  always  constantly  engaged,  and  conspiring  to  the  same 
end,  than  there  are  of  quadrupeds  in  existence  upon  the  whole 
surface  of  the  globe  !  The  above  are  designed  to  illustrate  the 
principles  of  the  argument  only  :  the  argument  itself,  like  all  the 
preceding  is  strictly  cumulative,  and  applies  more  or  less  to  every 
operation  in  nature. 

Such  is  a  summary  sketch  of  the  wonders  developed  by  che- 
mistry ;  and  what  an  idea  do  they  convey  to  us  of  the  wisdom 
and  of  the  power  of  Him  who  contrived  and  made  the  whole  !  Of 
the  capacity  of  that  eternal  Mind,  who  while  He  directs  the  uni- 
verse, at  the  same  time  takes  cognizance  and  regulates  the  move- 
ments of  every  individual  atom  in  it !  To  whom  the  inmost  nature, 
and  end,  and  object  of  every  part  are  familiar  ;  and  of  whose  com- 
prehensive designs  the  whole  forms  but  a  single  link,  the  antece- 
dent and  the  consequent  to  which  are  merged  alike  in  infinity  ! 


In  the  preceding  pages  we  have  pointed  out  a  few  of  those 
wonderful  arrangements,  which  to  common  understandings  appear 
to  indicate  design,  and  consequently  to  prove  that  such  arrange- 
ments are  the  works  of  an  intelligent  and  omnipotent  Creator. 
There  are  however  some  minds  so  obtuse,  or  so  strangely  con- 
stituted that  they  either  cannot,  or  will  not  admit  the  force  of  these 
arguments,  and  who  consequently  deny  the  evidences  of  design 
altogether.  The  consideration  of  this  part  of  the  subject  properly 
belongs  to  another  department,  to  which  the  reader  is  referred  for 
details  ;  we  shall  therefore  confine  our  observations  to  a  brief 
recapitulation  of  the  leading  objections  to  design,  and  offer  such 
answers  to  them  as  are  more  immediately  furnished  by  our  own 
subject. 

The  objectors  to  the  argument  of  design  may  be  divided  into 
two  classes  ;  those  who  denying  a  First  Cause,  affect  to  believe 
that  all  the  beautiful  adaptations  and  arrangements,  we  see  around 
us,  are  the  result  of  what  they  call  the  "  necessary  and  eternal 
laws  of  nature,"  and  who  in  fact  are  Atheists,  or  rather  Pantheists, 
"  to  whom  the  laws  of  nature  are  as  gods  ;"  and  those  who,  with- 
out denying  a  First  Cause,  contend  that  design  cannot  be /^roi'ef/,* 
that  the  arrangements  of  external  nature,  as  they  appear  to  us  are 
little  more  than  mental  delusions  ;  and  that  things  appear  congri^ 


112  CHEMISTRY. 

ous  and  adapted  to  us,  however  incongruous  they  may  be  in 
reality,  simply  because  we  have  nothing  else  than  our  own  intel- 
lects with  which  to  compare  them. 

To  the  first  class  of  objectors,  we  may  thus  briefly  reply.  The 
"  laws  of  nature,"  or  rather  our  knowledge  of  them,  may  be  con- 
sidered as  of  two  kinds ;  First,  laws  founded  upon  reason  or  ne- 
cessity, the  phenomena  regulated  by  which  laws  we  cannot  con- 
ceive to  be  otherwise  than  what  they  are  ;  and  laws  founded  upon 
eoq) erience  on\y ,  among  whose  dependant  and  sequent  phenomena 
we  can  discover  no  necessary  relation  whatever.  Now,  few,  if 
any,  of  the  "  laws  of  natiiie"  can  he  proved  to  belong  to  the  first 
kind ;  we  know  for  instance,  no  reason  or  necessity  why  hydro- 
gen, carbon,  oxygen,  and  azote  must  combine  to  form  plants  and 
animals  ;  we  only  know  that  they  do  so  combine,  but  why  and 
how  we  know  not.  Hence,  as  the  Atheist  cannot ^;?'oi'e  his  "  laws 
of  nature"  to  have  a  necessary  existence,  he  has  no  right  to  make 
the  assumption.  On  the  other  hand,  he  cannot  prove  these  laws 
to  be  eternal ;  for  experience,,  the  sole  ground  upon  which  his 
knowledge  of  them  is  founded,  is  decidedly  hostile  to  this  supposi- 
tion, as  we  have  in  the  next  place  briefly  to  show. 

In  reasoning  from  cause  to  effect  in  matters  of  experience,  two 
conditions  at  least  are  requisite  ;  first  the  efl^ect  must  be  possible, 
that  is  to  say,  must  not  be  opposed  in  any  way  to  the  cause,  or  to 
the  facts  of  the  argument;  and  secondly,  it  must  he  probable,  or 
in  other  words,  the  effect  must  accord  and  harmonize  generally 
with  the  accompanying  phenomena.  But  the  atheistical  doctrine 
of  the  "  eternal  laws  of  nature"  seems  to  us  to  violate  one,  if  not 
both  these  conditions.  In  the  first  place,  as  to  the  facts,  or  possi- 
bility of  the  case.  We  have  seen,  that  a  very  superficial  obser- 
vation of  the  world  as  it  exists,  and  as  it  obviously  has  existed 
within  the  limits  that  its  history  can  be  traced,  is  sufficient  to 
show,  that  its  course  at  all  times  has  been  progressive.  That  is 
to  say,  the  world  itself  before  arriving  at  its  present  condition,  has 
not  only  undergone  a  progressive  series  of  different  states ;  but  in 
these  different  states,  different  "laws  of  nature"  have  prevailed. 
In  the  second  place,  putting  the  previous  history  of  the  world  out 
of  the  question,  and  judging  solely  from  what  we  see  around  us, 
it  appears  improbable  in  the  highest  degree,  that  the  present  va- 
riable ^x\(\  finite  order  of  things,  should  constitute  a  term  or  link 
of  an  uniform  and  infinite  progression.  The  notion  therefore  that 
the  "  laws  of  nature"  have  existed  as  they  now  exist  from  eternity, 
if  not  actually  impossible,  is  so  exceedingly  improbable,  that  it 
cannot  be  admitted  for  a  moment.  Hence  as  these  laws  cannot 
be  proved  to  have  a  necessary  existence,  or  to  have  existed  from 
eternity  as  they  now  are;  it  becomes  more  than  probable  that  they 


OBJECTIONS  TO  DESIGN,  ETC.  113 

have   had  a  beginning  ;   and   thus  the  inference  of  a  pre-existent 
Law-maker,  and  all  its  consequences  are  at  once  inevitable. 

We  come  now  to  consider  the  second  class  of  objections  to  the 
argument  of  design  ;  those  namely,  which  are  founded  on  the 
grounds  that  design  cannot  be  jji'oved  ;  and  tliat  what  we  call  de- 
sign is  little  more  than  mental  delusion.  We  admit  at  once  that 
everything  we  know  of  external  nature  we  know  from  experience 
only  ;  and  consequently  we  admit  that  what  we  call  design  in  ex- 
ternal nature  is  only  very  probably  design  ;  that  is  to  say,  cannot 
be  proved  to  be  design  by  any  argument  founded  on  reason  or 
necessity.  But  liaving  made  this  admission,  we  assert  upon  the 
self-same  grounds,  that  our  opponents  cannot,  by  any  argument 
founded  on  reason  or  necessity,  prove  that  what  we  call  design, 
is  anything  else  than  design  ;  that  is  to  say,  is  not  design.  Now 
until  this  be  proved  the  force  of  their  objection  may  be  considered 
as  completely  neutralized;  while  the  objection  itself  becomes  thus 
reduced  to  the  condition  of  a  mere  sophism,  that  leaves  everything 
precisely  in  the  same  state  as  it  was  at  the  beginning. 

Having  thus  briefly  disposed  of  these  objections  to  the  argu- 
ment of  design,  we  finally  recur  with  pleasure  to  that  common- 
sense  view  of  the  subject  which  we  have  already  contended  for, 
and  which  we  still  maintain,  viz.,  that  design  is  independent  of 
the  designer  ;  in  other  words,  that  design  is  design,  whether  ex- 
emplified in  the  works  of  man  or  in  those  of  his  Maker — a  view 
which  has  been  adopted  by  the  wise  and  good  in  all  ages — which 
has  all  the  probabilities  on  iis  side,  and  which  alone,  of  all  others, 
points  out  to  man  his  true  and  natural  position  among  created  be- 
ings. When  man,  indeed,  compares  himself  with  the  universe, 
his  own  insignificance  appears  quite  overwhelming  ;  but  the  ar- 
gument of  design  assures  him  that,  insignificant  as  he  is,  while 
he  investigates  and  approves  of  the  order  and  harmony  around  him, 
he  is  exerting  faculties  truly  god-like — that  his  reason  though  li- 
mited in  degree,  must  be  immortal  in  kind,  and  thus  differ  from 
that  of  the  great  Architect  of  all,  only  in  not  being  infinite.  And 
hence  the  proud  relationship  in  which  man  justly  considers  him- 
self to  stand  with  respect  to  his  Maker  !  hence  the  grand  source 
of  that  longing  after  a  future  state,  where  his  knowledge  will  be 
consummated,  and  where  he  will  no  longer  "  see  through  a  glass 
darkly" — notions  at  once  the  result  and  reward  of  his  reason,  and 
which  raise  him  far  above  all  other  animals. 

10* 


114 


BOOK  II. 

OF  METEOROLOGY  :  COMPREHENDING  A  GENERAL  SKETCH  OF  THE  CONSTI- 
TUTION OF  THE  GLOBE  ;  AND  OF  THE  DISTRIBUTION  AND  MUTUAL  INFLU- 
ENCE OF  THE  AGENTS  AND  ELEMENTS  OF  CHEMISTRY  IN  THE  ECONOMY 
OF  NATURE. 

In  the  foregoing  chapters,  we  have  endeavoured  to  convey  some 
idea  of  the  "limits  which  the  Deity  has  been  pleased  to  prescribe 
to  his  own  power ;"  or  in  other  words,  of  the  properties  of  the 
different  subordinate  agents  and  elements  of  our  globe,  and  of 
their  mode  of  operation.  We  come  now  to  consider  a  little  more 
closely  the  general  distribution  of  these  agents  and  elements  ;  and 
the  principles  upon  which  this  distribution  is  regulated,  so  as  to 
produce  all  the  wonderful  results  which  we  see  constantly  going 
on  around  us  in  nature. 

In  the  present  state  of  the  world,  as  we  have  already  observed, 
the  general  tendency  of  its  constituent  principles  seems  to  be 
towards  a  state  of  equilibrium  or  repose.  But  a  very  superficial 
examination  of  those  parts  of  the  earth's  crust  to  whicli  we  can 
obtain  access,  is  sufficient  to  convince  us  that  this  quietude  has 
not  always  existed  ;  and  consequently  that  the  present  state  of 
things  must  have  had  a  beginning.  In  short  the  phenomena  of 
geology  appear  to  show,  that  our  earth  in  its  progress,  has 
undergone,  alternately,  periods  of  comparative  quietude  like  that 
in  which  we  now  live  ;  and  periods  of  derangement  and  convul- 
sion, in  which  the  preceding  stales  of  quietude  and  their  conse- 
quences have  been  more  or  less  subverted,  and  a  new  order  of 
things  has  been  induced.  To  enter  furllier  into  details  regarding 
these  changes,  however,  would  be  quite  foreign  to  the  object 
of  the  present  volume.  It  is  the  business  of  the  Geologist  to 
point  out  the  changes  w^hich  our  earth  has  evidently  undergone 
before  it  arrived  at  its  present  condition  ;  to  trace  the  earth  as  it 
were  from  a  stale  of  chaos  through  all  its  metamorphoses,  whether 
sudden  and  convulsive,  or  slow  and  gradual ;  and  to  show  that 
all  these  changes  have  not  resulted  from  chance,  but  from  the 
agency  of  an  intelligent  Being  operating  with  some  ulterior  pur- 
pose, and  according  to  certain  laws,  to  which  he  had  chosen  to 
restrict  himself — to  demonstrate,  in  short,  that  to  these  very  con- 
vulsions and  changes  we  owe  all  that  boundless  variety  of  sea 
and  of  land,  of  mountain  and  plain,  of  hill  and  valley  ;  all  that  endless 
admixture  of  rocks,  of  strata  and  of  soils,  so  essential  to  the  ex- 
istence of  the  present  order  of  things  ;  without  which  the  world 
would  have  been  a  mass  of  crystals,  or  one  dreary  monotonous 


RELATION  OF  SEA  TO  LAND.  115 

void,  totally  unfitted  for  the  present  race  of  organized  beings  ; 
and  particularly  as  a  residence  for  man — apparently  one  great 
end  and  object  of  creation.  Such  is  the  business  of  the  geolo- 
gist ;  and  where  his  duties  terminate,  those  of  the  Meteorologist 
may  be  said  to  begin.  To  him  it  belongs  more  especially  to 
consider  the  globe  in  [is  present  condition  of  quietude  or  equili- 
brium, and  the  means  by  which  this  state  of  equilibrium  is 
maintained :  in  particular,  to  point  out  the  influences  of  heat 
and  of  light,  and  of  the  energies  allied  to  them  ;  to  study 
the  laws  of  the  distribution  and  change  of  these  important  agents  in 
the  production  of  climate  ;  to  trace,  in  short,  the  effects  of  these 
wonderful  principles  upon  the  earth,  the  ocean,  and  the  atmo- 
sphere, and  all  the  infinite  variety  of  phenomena  dependent  upon 
them. 

In  so  wide  and  varied  a  field  of  inquiry  it  is  not  perhaps  easy 
to  devise  a  plan  that  shall  be  perfectly  unexceptionable.  For,  as 
there  is  no  one  subject  so  entirely  isolated,  as  not  to  be  more  or 
less  influenced  by  the  rest,  w^e  scarcely  know  which  to  commence 
with.  After  a  good  deal  of  reflection,  we  have  adopted  that  ar- 
rangement which  seems  to  ofler  the  most  natural  viev/  of  these 
subjects  :  and  at  the  same  time  appears  best  calculated  to  illus- 
trate the  design  and  wisdom  of  the  Great  Creator. 


CHAPTER  I. 

OF  THE  GENERAL  STRUCTURE  OF  THE  EARTH  :  PARTICULARLY  WITH  RE- 
FERENCE TO  THE  DISTRIBUTION  OF  ITS  SURFACE  INTO  LAND  AND  WA- 
TER ;    AND  WITH  RESPECT  TO  ITS  ATMOSPHERE. 

Section  I. 

Of  the  General  Relations  of  the  Sea  and  the  Land  to  each 

other. 

Our  earth  may  be  considered  as  made  up  of  materials  naturally 
existing  in  the  solid,  the  liquid,  and  the  gaseous  state,  the  abso- 
lute proportions  of  whicji  to  each  other  we  cannot  even  conjecture. 
Of  the  mean  density  of  the  whole,  however,  we  can  form  some 
estimate  ;  and  philosophers  have  shown  that  this  density  lies 
between  five  and  five  and  a  half,  that  of  Avater  being  one.  We  can 
also  form  a  tolerably  precise  notion  of  the  relative  proportions  of  the 
surface  occupied  by  the  solid  and  the  liquid  materials  ;  and  of  the 
pressure  and  height  of  the  atmosphere  surrounding  the  whole. 

With  the  general  geographical  distribution  of  land  and  ocean, 


116  METEOROLOGY. 

we  take  it  for  granted  that  all  are  more  or  less  acquainted.  We 
shall,  therefore,  confine  our  remarks  chiefly  to  their  relative  pro- 
portions ;  which  are  such,  that  nearly  three-fourths  of  the  earth's 
surface  may  be  said  to  be  covered  with  water,  while  barely  one- 
fourth,  of  course,  must  be  occupied  by  dry  land.  Of  this  dry 
land,  as  is  well  known,  by  far  the  greater  part  is  confined  to  the 
northern  hemisphere  ;  while  in  the  southern  hemisphere,  the 
Pacific  ocean  exhibits  a  nearly  continuous  surface  of  water,  greater 
than  the  whole  dry  land  of  the  globe  put  together.  According  to 
the  estimate  of  Humboldt,  the  dry  land  in  the  two  hemispheres 
is  in  the  ratio  of  three  to  one ;  between  the  tropics  in  the  two 
hemispheres  as  five  to  four  ;  and  without  the  tropics  as  thirteen 
to  one  ;   the  preponderance  being  in  the  northern  hemisphere. 

The  height  of  the  dry  land  above  the  general  level  of  the 
ocean  is  very  various  ;  but  its  utmost  height,  as  compared  with 
the  diameter  of  the  earth,  is  quite  trifling  ;  and  it  has  been  shown 
that  if  the  whole  of  the  dry  land  existing  were  equally  distributed 
over  the  bottom  of  the  sea,  the  quantity  of  water  in  the  sea  is 
amply  sufficient  to  cover  it  entirely.  Hence  "dry  land  can  be 
only  considered  as  so  much  of  the  rough  surface  of  our  globe  as 
may  happen  for  the  time  to  be  above  the  level  of  the  waters  ; 
beneath  which  it  may  again  disappear,  as  it  has  done  at  diflerent 
previous  periods."* 

The  solid  portions  of  our  earth  are  all  made  up  of  various 
combinations  of  the  elementary  principles  described  in  a  former 
chapter.  The  relative  situations  these  principles  occupy  in  the 
earth's  structure  ;  the  endless  proportions  in  which  they  exist ; 
and  all  the  infinite  diversity  of  their  properties,  it  is  the  business 
of  the  geologist  and  of  the  mineralogist  to  inquire  into  and  ex- 
plain :  the  observations,  therefore,  which  we  have  to  make  on 
the  present  part  of  our  subject,  will  be  chiefly  confined  to  the 
waters  of  the  ocean,  and  to  the  atmosphere. 


Section  H. 

Of  the  Ocean. 

The  waters  of  the  ocean  are  not  pure,  but  contain, as  is  well- 
known,  a  variety  of  saline  matters  in  solution.  Indeed,  when  we 
reflect  upon  the  immense  relative  extent  and  general  circumstances 
of  the  ocean,  we  may  naturally  suppose  that  its  waters  will  con- 
tain more  or  less  of  every  existing  soluble  principle.  By  far  the 
most  abundant  principle,  however,  in  sea-water  is  common  salt  ; 

•  De  la  Bcche's  Geological  Manual  p.  2. 


OF  THE  OCEAN.  1  17 

which  may  be  said  to  constitute,  in  general,  nearly  two-thirds  of 
the  whole  saline  matter  present.  The  saline  matter  lluctuates 
between  three  or  four  per  cent ;  and  the  specific  gravity  of  the 
water  varies,  according  to  the  proportion  of  the  saline  ingredients, 
from  about  1026  to  1030;  pure  water  being  supposed  to  be  1000. 
The  late  Dr.  Marcet,  some  years  ago,  made  some  interesting 
experiments  on  this  subject,  and  the  following  are  the  general 
conclusions  which  he  drew  from  them  : — 

1.  That  the  southern  ocean  contains  more  salt  than  the 
northern  ocean,  in  the  ratio  of  1.02919  to  1.02757. 

2.  That  the  mean  specific  gravity  of  sea-water,  near  the 
equator,  is  1.02777;  or  intermediate  between  that  of  the 
northern  and  that  of  the  southern  hemispheres. 

3.  That  there  is  no  notable  difference  in  sea-water  under 
different  meridians. 

4.  That  there  is  no  satisfactory  evidence  that  the  sea  at 
great  depths  is  more  salt  tlian  at  the  surface. 

5.  That  the  sea,  in  general,  contains  more  salt  where  it 
is  deepest  and  most  remote  from  land  ;  and  that  its  sahness 
is  always  diminished  in  the  vicinity  of  large  masses  of  ice. 

6.  That  small  inland  seas,  though  commmiicating  with 
the  ocean,  are  much  less  salt  than  the  ocean. 

7.  That  the  Mediterranean  contains  rather  larger  propor- 
tions of  salt  than  the  ocean.* 

The  saltness  of  the  sea,  therefore,  is  considerably  influenced, 
at  least  at  its  surface,  by  the  neighbourhood  of  large  rivers,  and 
by  permanent  accumulations  of  ice  ;  and  in  this  way  the  inferior 
saltness  of  small  inland  seas,  particularly  in  high  latitudes,  may 
in  general  be  explained,  as  most  of  these  inland  seas  are  supplied 
with  comparatively  large  quantities  of  fresh  water  from  the  rivers 
flowing  into  them.  On  the  other  hand,  the  superior  saltness  of 
the  Mediterranean  has  been  ascribed  to  the  immense  evaporation 
from  its  surface ;  the  consequence  principally  of  its  being  situated 
in  a  warmer  climate. 

The  saline  contents  of  the  ocean  are  of  immense  importance 
in  the  economy  of  nature.  Such  indeed  is  their  importance,  that 
it  is  doubtful  whether  the  present  order  of  things  could  be  main- 
tained without  them.  Tiie  efl^ects  of  these  saline  matters  will  be 
more  particularly  pointed  out  hereafter.  In  this  place  we  shall 
only  remark,  that  by  lowering  the  freezing  point  of  water;  and 
by  diminishing  its  tendency  to  give  ofl*  vapour,  they  perform  the 
most  beneficial  oflices.  Another  valuable  purpose  which  they 
serve  may  be  alluded  to  here,  viz.  the  greater  power  of  buoyancy 
which  they  communicate  to  water;  by  means  of  which  the  wa- 

*  Philos.  Trans.  1819. 


118  3IETE0R0L0GY. 

ters  of  the  ocean  are  belter  fitted  for  the  purposes  of  navigation. 
Nor  are  these  the  only  uses  of  the  saline  matters  ;  for  there  is 
reason  to  believe  that  they  contribute  in  no  small  degree  to  the 
stability  of  the  water  ;  and  that  an  ocean  of  fresh  water  would 
speedily  undergo  changes  that  would  probably  render  it  incom- 
patible with  animal  life  ;  such  an  ocean  perhaps  would  even  suffer 
decomposition,  that  might  seriously  interfere  with  the  other  ar- 
rangements of  nature. 

Lastly,  who  will  venture  to  assert  that  the  distribution  of  sea 
and  of  land,  as  they  now  exist,  though  apparently  so  dispropor- 
tionate, is  not  actually  necessary  as  the  world  is  at  present  con- 
stituted ?  What  would  be  the  result,  for  instance,  if  the  Pacific 
or  the  Atlantic  oceans  were  to  be  converted  into  continents  ? 
Would  not  the  climates  of  the  existing  continents,  as  formerly 
observed,  be  completely  changed  by  such  an  addition  to  the  land, 
and  the  whole  of  their  fertile  regions  be  reduced  to  arid  deserts  ? 
Now,  this  distribution  of  sea  and  of  land,  so  wonderfully  adapted 
as  it  appears  to  be  to  the  present  state  of  things,  depends  of 
course  in  a  great  measure  upon  the  absolute  quantity  of  water 
in  the  world.  While  on  the  other  hand,  the  relative  gravity  of 
water  as  compared  with  that  of  the  earth,  keeps  the  ocean  within 
its  destined  limits,  notwithstaudino:  its  incessant  motion.  Thus 
Laplace  has  shown  that  the  world  would  have  been  constantly  liable 
to  have  been  deluded  from  the  slightest  causes,  had  the  mean  den- 
sity  of  the  ocean  exceeded  that  of  the  earth  !  Hence  the  adjust- 
ment of  the  quantity  of  water  and  of  its  density,  as  compared 
with  that  of  the  earth,  afford  some  of  the  most  marked  and  beau- 
tiful instances  of  design. 


Section  IIL 

Of  the  Atmosphere. 

That  immense  body  of  gaseous  matters  surrounding  our 
earth,  and  usually  known  under  the  name  of  the  Atmosphere, 
is  essentially  composed,  as  we  formerly  stated,  of  two  princi- 
ples, oxygen  and  azote,  in  the  proportion  nearly  of  one  part  of 
oxygen  and  four  parts  of  azote.  13esides  these  two  gases,  the 
atmosphere  also  contains  a  small  and  perhaps  a  variable  quantity 
of  carbonic  acid  gas,  amounting  upon  an  average  to  about  one 
part  in  a  thousand  of  the  whole  ;  and  of  water  in  a  state  of  va- 
pour, likewise  a  variable  quantity,  (as  will  be  shown  iiereafter,) 
but  usually  fiuctuating  between  one,  and  one  and  a  half  per  cent. 
In  addition  to  these,  there  are,  probably  also  other  matters  con- 
stantly present  in  the  atmosphere  ;  for  as  the  sea  contains  a  little 


OF  THE  ATMOSPHERE.  119 

of  everything  that  is  soluble  in  water,  so  the  atmosphere  may  be 
conceived  to  contain  a  little  of  everything  that  is  capable  of  as- 
suming the  gaseous  form. 

The  atmosphere  exerts  a  pressure  or  weight  upon  all  parts  of 
the  earth's  surface,  on  an  average  equal  to  about  fifteen  pounds 
upon  a  square  inch  ;  or  in  other  words,  equal  in  weight  to  a  co- 
lumn of  mercury  one  inch  square  and  thirty  inclies  high.  The 
well-known  instrument  the  common  Barometer  ox  JVealJicr-glass, 
consists  of  nothing  more  than  such  a  column  of  mercury,  poised 
or  pressed  upw-ards  into  a  vacuum,  by  the  weight  of  tlie  atmo- 
sphere. With  the  changes  constantly  taking  place  in  the  height 
of  such  a  column,  every  body  is  familiar,  and  we  shall  have  oc- 
casion to  recur  to  tliem  hereafter;  at  present  it  is  only  requisite 
to  observe,  tliat  these  changes  are  much  less  remarkable  in  tropi- 
cal than  in  temperate  climates.  Thus,  between  the  tropics  the 
barometer  usually  varies  only  about  one- third  of  an  inch  ;  while 
in  temperate  climates,  the  changes  amount  to  upw^ards  of  one- 
tenth  of  the  whole  heio^ht. 

The  pressure  of  the  atmosphere  decreases  as  we  ascend  above 
the  earth's  surface  ;  and  for  equal  ascents,  this  decrease  of  density 
is  in  what  is  called  geometrical  progression.  Thus,  at  three 
miles  in  height,  the  density  of  the  atmosphere  is  only  one-half 
of  what  it  is  at  the  surface  of  the  earth,  or  equal  to  a  column  of 
mercury  fifteen  inches  in  height ;  at  six  miles,  the  barometer 
would  stand  at  one-fourth  of  its  usual  height,  or  seven  and  a  half 
inches  ;  at  nine  miles  of  elevation,  at  three  inches  and  three 
quarters  ;  and,  at  fifteen  miles,  nearly  at  one  inch  only.  Hence 
by  far  the  greater  portion  of  the  atmosphere  is  always  within  fif- 
teen or  twenty  miles  of  the  earth's  surface  ;  though  tVom  various 
circumstances  it  lias  been  inferred  to  extend  from  forty  to  forty- 
five  miles  in  height.  This  height,  however,  must  be  different  in 
different  latitudes  ;  for  the  rotation  of  the  earth  npon  its  axis,  and 
the  greater  and  more  direct  influence  of  the  solar  heat  npon  the 
earth's  equatorial  regions,  will  necessarily  cause  the  atmosphere 
to  be  higher  there  than  in  the  polar  regions  ;  at  the  poles,  the  at- 
mosphere must  be  lower  than  over  any  other  part  of  the  earth's 
surface.  These  are  most  important  circumstances  in  the  economy 
of  nature,  as  we  shall  see  hereafter. 

Much  difference  of  opinion  has  existed  among  philosophers  as 
to  the  mode  in  which  the  various  principles  entering  into  the  com- 
position of  atmospheric  air  are  associated  ;  some  maintaining  that 
these  principles  exist  simply  in  a  state  of  mixture  :  others  consi- 
dering them  as  chemically  united.  We  formerly  stated  that  all 
gaseous  bodies,  when  they  combine  witfi  one  another,  combine 
with  reference  to  their  volumes  ;  that  is  to  say,  that  on3  volume 
of  one  gas  always  combines  with  one,  two,  or  more  similar  vol- 


120  METEOROLOGY. 

umes  of  the  same,  or  of  another  gas,  and  not  with  any  inter- 
mediate fractional  part.  Now,  as  atmospheric  air  is  composed 
essentially  of  one  volume  of  oxygen  and  four  volumes  of  azote, 
it  is  evident,  whether  its  elements  be  in  actual  union  or  not,  that 
it  is  at  least  constituted  upon  strictli/  chemical  principles  ; 
whence  it  follows,  that  the  composition  of  the  atmosphere  has 
not  been  the  result  of  accident.  In  this  point  of  view,  therefore, 
atmospheric  air  may  be  considered  to  be  as  much  a  chemical  com- 
pound as  water,  or  any  other  similar  body  ;  and  instead  of  viewing 
the  atmosphere,  according  to  a  prevalent  notion,  as  a  mere  acci- 
dental and  heterogeneous  appendage  connected  with  the  denser 
matters  by  no  apparent  tie,  we  may  fairly  rank  the  atmosphere 
among  the  constituent  principles  of  our  globe,  and  as  forming  a 
symmetrical  part  of  the  great  harmonious  whole. 

But  although  atmospheric  air  has  been  thus  originally  constituted 
upon  chemical  principles,  and  probably  owes  to  this  circumstance, 
in  no  small  degree,  its  stability;  yet  the  mode  in  which  its  con- 
stituent elements  are  associated,  is  very  different  from  that  in  which 
the  elements  of  compounds  in  general  are  associated.  Indeed  the 
constituent  elements  of  atmospheric  air  do  not  appear  to  be  com- 
bined at  all ;  but  to  be  only  mixed,  or  simply  diffused  through 
each  other,  in  the  same  manner  that  the  minute  portions  of  car- 
bonic acid  gas  and  of  vapour  are  known  to  be  difiused  through 
the  whole  atmosphere ;  that  is  to  say,  according  to  the  laws  of  the 
Sfeneral  diffusion  of  graseous  bodies  M'hich  we  endeavoured  to 
explain  in  a  former  chapter.  To  this  explanation  we  must  refer 
the  reader  for  details.  We  shall  merely  observe  here,  that  the 
fundamental  principle  of  this  explanation  consists  in  the  assump- 
tion, that  the  molecules  of  all  bodies  in  the  gaseous  slate  are 
self-repulsive  (or  repulsive  of  one  another,  in  preference  to  others), 
for  the  same  reason  that  in  the  solid  state  they  are  self-attractive 
(or  attract  one  another,  in  preference  to  others).  When  diiTerent 
gaseous  bodies  therefore,  are  mixed  together,  t!iey  will  not  assume 
a  position  according  to  their  specific  gravities,  as  they  might  other- 
wise be  expected  to  do  ;  but  the  molecules  of  each  gas  will  be 
equally  diffused  throughout  the  whole  space  occupied  by  the 
mixture.  Hence,  one  direct  and  most  important  effect  of  the 
mixed  constitution  of  the  atmosphere,  is  its  nearly  uniform  com- 
position^ at  least  within  the  limits  attainable  by  man — a  fact  that 
has  been  confirmed  by  innumerable  analyses  of  the  air,  made  in 
all  parts  of  the  world,  both  at  its  surface  and  at  the  greatest  heights 
hitherto  reached.  Moreover,  this  constitution  of  the  atmosphere 
not  only  originally  produced  such  uniformity  of  composition,  but 
it  is  the  cause  constantly  operating  to  preserve  that  uniformity 
— the  grand  conservative  principle,  as  it  were,  preventing  any 
unequal  distribution  of  the  constituent  elements  of  the  atmosphere, 
which  would  speedily  prove  fatal  to  organic  life !  Were  the  ga- 


OF  THE  ATMOSPHERE.  121 

seoiis  principles  composing  the  atmosphere  in  ever  so  slight  a 
state  of  union,  they  could  not  readily  difluse  themselves  through 
each  other;  and  partial  accumulations  of  one  or  other  of  them 
would  be  constantly  taking  place  ;  but  as  the  atmosphere  is  at 
present  constituted,  if  a  little  more  oxygen  be  consumed  in  one 
spot  than  in  another,  instantly  the  deficiency  is  supplied  from  the 
neighbourhood  by  diffusion,  and  the  equilibrium  is  scarcely  af- 
fected in  a  sensible  degree.  Another  curious  result  of  tliis  inde- 
pendent condition  of  the  gaseous  principles  of  the  atmosphere  is, 
that  of  the  whole  pressure  exerted,  each  principle  exerts  its  own 
force  according  to  its  quantity.  Thus,  of  the  thirty  inches  of 
mercury  supported  by  the  whole  atmospheric  pressure,  the  azote 
sustains  23  j^/q-  inches,  and  the  oxygen  6  -^-^^  inches  ;  while  the 
aqueous  vapour  sustains  only  -^^^  inch,  and  the  carbonic  acid  still 
less,  or  only  yfo-  inch.  Hence  it  is  evident  that  the  fluctuations 
in  the  height  of  the  barometer,  amounting  to  nearly  three  inches 
in  our  latitude,  cannot  depend  altogether  upon  the  quantity  of 
aqueous  vapour  in  the  atmosphere  ;  for  if  the  whole  of  this  vapour 
were  annihilated,  it  would  scarcely  produce  a  difference  in  height 
of  half  an  inch.  Attention  is  now  drawn  to  this  fact  for  purposes 
that  will  appear  in  a  subsequent  chapter. 

Lastly,  had  the  absolute  quantity,  or  the  relative  gravity,  of  the 
atmosphere  been  materially  different  from  what  they  are,  the 
present  order  of  things  could  not  have  existed.  Hence,  the  same 
striking  evidences  of  wise  adjustments  are  displayed  in  these  ar- 
rangements of  the  atmosphere,  as  in  those  formerly  shown  to 
exist  with  respect  to  the  quantity  and  gravity  of  the  ocean. 

Before  we  close  the  present  chapter,  let  us  reflect  for  a  mo- 
ment upon  the  great  arrangements  we  have  been  considering. 

Why  has  the  surface  of  this  earth  been  divided  into  land  and 
sea?  Why  have  the  land  and  sea  been  so  adjusted  to  each  other, 
that  their  condition  and  properties  hardly  admit  of  change  with- 
out destruction  to  the  whole  fabric  ?  Why  has  their  present 
stability  been  so  wonderfully  secured  !  Again,  with  respect  to 
the  atmosphere  ;  why  has  there  been  any  atmosphere  thrown 
around  this  globe  ?  and  why  sucli  manifest  provisions  to  secure 
its  ubiquity  and  unvarying  constitution  ? 

Viewed  alone  and  without  reference  to  organized  beings,  all 
these  things  appear  without  an  object.  This  globe  might  have 
revolved  about  the  central  luminary — might  have  occupied  its 
point  in  the  universe  without  any  "  gathering  together  of  the 
waters,"  w^ithout  any  circumambient  air.  But  the  scheme  of  the 
great  Creator  extended  beyond  the  mere  adaptation  of  inanimate 
matter.  "  Before  its  foundations  were  laid,"  He  had  destined 
this  earth  to  teem  with  life,  and  throughout  has  displayed  his 
original  design  of  rendering  it  a  fit  habitation  for  living  beings. 

11 


122  METEOROLOGY. 

For  this  purpose  and  acting  at  tiie  same  time,  in  strict  conformity 
to  those  laws,  by  which  He  had  chosen  to  Uaiit  himself.  He  has, 
by  means  of  successive  convulsions  and  changes,  so  contrived  to 
mix  and  blend  the  different  elements,  and  finally  so  to  arrange 
the  dry  land  apart  from  the  sea ;  that,  taken  as  a  whole,  and  with 
reference  to  the  present  order  of  things,  their  relative  proportions 
will  scarcely  admit  of  material  change.  While,  to  crown  his 
works,  and  as  it  were,  the  more  strongly  to  evince  his  design, 
and  his  wisdom,  He  has  surrounded  the  whole  with  an  atmo- 
sphere, to  preserve  the  homogeneity  of  which,  its  principles  have 
been  so  associated,  as  to  constitute  an  exception  to  his  usual  ope- 
rations, and  even  to  the  general  laws  of  nature  ! 


CHAPTER  n. 

OF    HEAT    AND    LIGHT THE    BIODES  OF  ESTIMATING    THEIR    DEGREE,    AND 

THE  WAYS  IN  V»'HICH  THEY  ARE  PROPAGATED.  OF  THE  GENERAL 
TEMPERATURE  OF  THE  CELESTIAL  REGIONS,  AND  OF  THE  EARTH  INDE- 
PENDENTLY OF  THE  SUN. 

Section  I. 
Of  Heat  and  Light,  and  the  Modes  of  estimating  their  Degree. 

Our  sensations  are  a  very  imperfect  and  uncertain  measure  of 
temperature,  and  when  we  wish  to  speak  with  precision  on  that 
subject,  it  becomes  necessary  to  have  recourse  to  other  means  of 
comparison.  For  the  sake  of  the  general  reader,  we  shall,  there- 
fore, in  the  first  phice,  briefly  describe  the  principles  of  the  con- 
struction of  the  Thermometer,  the  instrument  for  measuring  heat. 

All  bodies,  as  we  have  shown  in  a  former  chapter,  become 
more  or  less  expanded  when  they  undergo  an  increase  of  temper- 
ature. Hence  the  relative  degrees  of  expansion  of  a  body  may 
be  employed  as  a  sort  of  measure  of  the  degree  of  heat ;  and  most 
of  the  thermometers  employed,  act  upon  this  principle.  Thus 
the  common  thermometer,  as  is  Avell  known,  consists  of  a  portion 
of  some  fluid,  generally  of  mercury,  enclosed  in  a  small  glass  ball 
furnished  with  a  hollow  stem,  the  narrow  bore  of  which  commu- 
nicates with  the  general  cavity  of  the  ball.  We  shall  suppose 
the  quantity  of  the  mercury,  and  the  size  of  the  ball,  to  be  so  ad- 
justed to  each  other,  that  when  the  instrument  is  placed  in  ice  on 
the  one  hand,  and  in  boiling  water  on  the  other,  the  whole  ex- 
pansion of  the  mercury  between  these  two  fixed  points,  shall  fall 
within  the  range  of  the  stem  or  tube.     The  points  at  which  the 


PROPAGATION  OF  HEAT  AND  LIGHT.  123 

mercury  stands  in  the  tube,  at  the  freezing  and  boiling  tempera- 
tures are  to  be  accurately  noted;  and  the  intermediate  space  upon 
the  scale  attached  to  tiie  tube,  is  to  be  divided  into  180  equal 
parts  or  degrees  ;  the  freezing  point  is  to  be  marked  32°,  and  of 
course,  the  boiling  point  180°  above,  or  212°.  Such  is  Fahren- 
heiVs  scale,  the  one  employed  in  this  country,  and  to  which  the 
numbers  hereafter  mentioned  refer.  In  other  countries  different 
scales  are  made  use  of;  and  in  France  particularly,  what  is  termed 
the  centigrade  thermometer  is  generally  adopted.  In  this  ther- 
mometer the  freezing  point  is  marked  0°  and  the  boiling  point 
100.  In  other  parts  of  the  continent  Beaimiur^s  scale  is  much 
used.  In  Reaumur's  the  freezing  point,  as  in  the  Centigrade,  is 
0°,  but  the  boiling  point  is  only  80°.  These  different  gradua- 
tions are  easily  convertible,  but  it  is  much  to  be  regretted  that 
they  exist,  as  they  cause  considerable  trouble  and  confusion. 

The  instrument  employed  for  measuring  the  intensity  of  light 
is  termed  a  Photometer  ;  of  such  an  instrument  various  forms  have 
been  proposed,  but  at  present  they  are  all  very  imperfect. 


Section  II. 
Of  the  Propagation  of  Heat  and  Light. 

The  modes  in  which  heat  and  light  are  propagated  from  one 
body  to  another,  and  through  the  same  body,  have  been  already 
explained,  and  we  need  not  again  enter  into  details  :  a  brief  recital 
here,  however,  of  the  modes  in  which  heat  and  light  are  propa- 
gated, may  not  be  unacceptable  to  the  general  reader. 

Heat  passes  from  the  sun  to  the  earth  by  radiation  ^  and  again, 
by  the  same  process,  it  is  freely  sent  off  from  the  surface  of  the 
earth  into  the  atmosphere.  Below  the  surface  of  the  earth,  heat 
is  propagated  in  all  directions  through  the  solid  matter,  by  what 
is  called  conduction.  A  third  mode  in  which  this  important  agent 
is  extensively  propagated  in  nature,  is  by  the  means  we  have 
termed  convection,  or  the  carrying,  "process.  Convection  is  con- 
fined, of  course,  to  fluids,  as  water  and  air.  A  portion  of  water 
or  of  air  being  heated  above,  or  cooled  below  the  surrounding 
portions,  expands  or  contracts  in  magnitude,  and  thus  becoming 
specifically  lighter  or  heavier,  rises  or  sinks  accordingly;  carry- 
ing with  it,  the  newly  acquired  temperature,  whatever  that  tem- 
perature may  be. 

Light,  at  present,  is  only  known  to  be  propagated  by  radiation. 

By  bearing  in  mind  these  modes  of  the  propagation  of  heat  and 
light,  the  general  reader  will  find  no  difficulty  in  understanding 
what  follows. 


124  METEOROLOGY. 

Section  III. 

Of  the  Temperature  of  the  Celestial  Regions. 

From  tlie  close  and  intimate  relations  between  heat  and  light, 
and  from  their  almost  invariable  association  as  they  exist  around 
lis,  it  seems  not  very  unreasonable  to  conclude  that  these  agencies 
are  generally  associated  in  nature  ;  and  that  wherever  one  is  pre- 
sent, there  the  other  must  be  present  also.  If  this  be  really  the 
case,  the  innumerable  fixed  stars,  considered  to  be  so  many  suns, 
must  be  supposed  capable  of  diffusing  heat  as  well  as  light  through- 
out the  celestial  regions  ;  and  consequently  there  must  be  a  certain 
degree  of  temperature  common  to  the  whole.  For  this  reason, 
and  for  others  that  might  be  mentioned,  philosophers  have  not 
only  inferred  the  existence  of  such  a  common  temperature  exist- 
ing throughout  the  celestial  regions,  independently  of  our  sun ; 
but  have  even  attempted  to  determine  its  degree.  Moreover,  it  is 
singular  that  all  the  diflerent  modes  which  have  been  employed  to 
estimate  this  temperature,  concur  in  showing  that  it  does  not  differ 
much  from — 58°  of  Fahrenheit's  scale  ;  that  is  to  say,  about  90° 
below  the  freezing  point  of  water ;  a  degree  of  cold  '*  not  greatly 
inferior  to  that  at  which  quicksilver  becomes  solid,  and  much  su- 
perior to  some  degrees  of  cold  which  have  been  produced  artifici- 
ally."* If  such  a  common  temperature  really  exists  throughout 
space,  or  at  least  in  our  planetary  system,  it  must  have  no  incon- 
siderable influence  upon  the  temperature  of  the  planets  generally  ; 
and  with  respect  to  our  own  globe  in  particular,  such  a  common 
temperature  must  operate  by  diminishing  the  intensity  of  the  cold 
around  the  poles. 

Section  IV. 

Of  the  Temperature  of  the  Interior  of  the  Earth. 

The  attention  of  philosophers  has,  for  some  years  past,  been  a 
good  deal  directed  to  the  internal  temperature  of  the  earth,  at  great 
depths,  beyond  the  influence  of  the  sun  or  of  any  other  external 
cause.  From  the  earliest  times  some  vague  notions  of  a  central 
heat  seem  to  have  existed  among  mankind  ;  doubtless,  arising 
from  their  attention  being  forcibly  drawn  to  the  phenomena  of 

•  Discovirsc  on  the  Study  of  Natural  Philosophy  ;  p.  157.  By  Sir  J.  F. 
W.  Herschcll. 


HEAT  OF  THE  INTERIOR  OF  THE  EARTH.  125 

volcanoes  and  hot  springs  ;  but  it  is  not  till  a  comparatively  late 
period  that  the  subject  has  been  carefully  investigated.  It  would 
be  quite  foreign  to  our  design  to  enter  here  into  details  upon  this 
point ;  we  shall  therefore  merely  state,  that  the  arguments  in  favour 
of  the  probability  of  a  central  heat  are — "  first,  the  experiments 
made  in  mines,  which,  notwithstanding  their  liability  to  error  from 
various  sources,  still  seem  to  show,  particularly  those  made  in  the 
rock  itself,  an  increase  of  temperature  from  the  surface  down- 
wards ; — secondly,  the  existence  of  thermal  springs,  wliich  are 
not  only  abundant  among  active  and  extinct  volcanoes,  but  also 
among  all  varieties  of  rocks  in  various  parts  of  the  world ; — 
thirdly,  the  existence  of  volcanoes  themselves,  wliich  are  distri- 
buted over  the  globe,  and  present  such  a  general  resemblance  to 
each  other  that  they  may  be  considered  as  produced  by  a  common 
cause,  and  that  cause,  probably,  deep-seated  ; — and  lastly,  the  ter- 
restrial temperature  at  comparatively  small  depths,  which  does  not 
coincide  with  the  mean  temperature  of  the  air  above  it."* 

Such  is  an  abstract  of  the  principal  arguments  which  have  been 
brought  forward  in  support  of  the  opinion,  that  within  our  earth, 
even  at  the  present  time,  there  exists  a  central  heat  of  great  inten- 
sity. As  corroborative  of  the  same  views,  may  be  mentioned  the 
evidence  derived  from  the  characters  of  the  fossil  remains  both  of 
plants  and  of  animals,  found  in  the  colder  regions  of  the  woilJ  ; 
which  ciiaracters  are  such  as  to  prove  beyond  a  doubt,  that  these 
plants  and  animals  must  have  existed  in  a  climate  much  hotter 
than  that  in  which  their  remains  are  found,  and  indeed,  of  equal, 
if  not  of  superior,  heat  to  that  of  the  tropical  portions  of  our  earth 
at  this  time.  Hence  it  has  been  inferred,  that  the  temperature  of 
our  earth,  formerly  much  above  M^iat  it  is  now,  has  been  giadu- 
ally  dissipated  into  the  surrounding  planetary  regions,  and  tlius 
helped  to  increase  the  general  temperature,  above  stated,  as  sap- 
posed  to  exist  throughout  space.  Moreover,  the  same  distinguished 
philosopher,!  to  whom  we  are  principally  indebted  for  these  ob- 
servations, has  attempted  to  show  that  the  earth  has  nearly  reached 
its  limit  of  cooling,  particularly  near  the  surface.  Near  the  surface 
the  temperature  would  necessarily  decrease  much  more  rapidly 
than  in  llie  interior  ;  where,  in  a  globe  of  the  earth's  magnitude, 
the  temperature  might  be  supposed  to  remain  nearly  unchanged 
for  a  very  great  length  of  time.  He  has  also  attempted  to  show 
that  the  temperature  of  the  surface  is  still  liable  to  be  influenced, 
by  the  gradual  escape  of  heat  from  the  interior  which  even  yet 
seems  to  be  constantly  going  on  ;  and  that  the  temperature  of  the 
surface  is  thus  somewhat  higher  than  it  would  be  if  such  a  central 

*  De  la  Beche's  Geolog-'ical  Manual,  p.  24,  new  ed. 
f  Baron  Foiu-ier. 

II* 


126  METEOROLOGY. 

heat  did  not  exist ;  or  than  if  the  temperature  of  the  surface  of  the 
earth  depended  only  upon  the  action  of  the  sun.  And  this  brings 
us  to  the  point  at  which  our  subject  may  be  said  properly  to  be- 
gin, viz.  the  consideration  of  the  present  state  of  the  earth's  tem- 
perature, as  liable  to  be  influenced  by  the  presence  or  absence  of 
the  sun,  the  great  source  of  heat  and  of  life  to  our  system. 

Before  proceeding,  we  may  remark,  that  the  details  of  the  sub- 
ject we  have  now  concluded,  fall  entirely  within  the  province  of 
the  geologist.     To  him  it  belongs,  as  we  have  already  said,  not 
only  to  trace  the  wonderful  changes  which  our  globe  has  under- 
gone in  arriving  at  its  present  condition,  but  to  point  out  the  beau- 
tiful adaptations  of  organic  life  and  structure  to  the  existing  cir- 
cumstances of  its  various  epochs.     Considered  in  this  point  of 
view,  geology  is  a  subject  of  the  highest  interest  and  importance; 
and,  to  use  "the  words  of  an  eminent  Professor,  with  which  we 
shall  finish  this  chapter,  "  lends  a  great  and  unexpected^aid  to  the 
doctrine  of  final  causes  ;  for  it  has  not  merely  added  to  the  cumu- 
lative argument,  by  the  supply  of  new  and  striking  instances  of 
mechanical  structure  adjusted  to  a  purpose,  and  that  purpose  ac- 
complished ;  but  it  has  also  proved  that  the  same  pervading  active 
principle  manifesting  its  power  in  our  times,   has  also  manifested 
its  power  in  times  long  anterior  to  the  records  of  our  existence. 

*'  But,  after  all,"  continues  our  author,  "  some  men,  seeing  no- 
thing but  uniformity  and  continuity  in  the  works  of  nature,  have 
still  contended  (with,  what  I  think,  a  mistaken  zeal  for  the  honour 
of  sacred  truth)  that  the  argument  from  final  causes  proves  nothing 
more  than  a  quiescent  intelligence.  I  feel  not  the  force  of  this 
objection.  In  geology,  however,  w^e  can  meet  it  by  another  di- 
rect argument ;  for  we  not  only  find  in  our  formations  organs  me- 
chanically constructed,  but  at  diff'erent  epochs  in  the  history  of 
the  earth  we  have  great  changes  of  external  conditions,  and  cor- 
responding changes  of  organic  structure  ;  and  all  this  without  the 
shadow  of  a  proof  that  one  system  of  things  graduates  into,  or  is 
the  necessary  and  efilcient  cause,  of  the  other.  Yet  in  all  these 
instances  of  change,  the  organs,  as  far  as  we  can  comprehend  their 
use,  are  exactly  those  which  were  best  suited  to  the  functions  of 
the  being.  Hence,  we  not  only  show  intelligence  contriving  means 
adapted  to  an  end,  but  at  successive  times  and  periods  contriving 
a  change  of  mechanism  adapted  to  a  change  in  external  conditions. 
If  this  be  not  the  operation  of  a  prospective  and  active  intelligence, 
where  are  we  to  look  for  it?"* 

*  Address  delivered  to  the  Geolog-icul  Society  of  London,  by  the  late 
President,  Professor  Sedg-wick,  1831. 


127 


CHAPTER  III. 

OF  THE  TEMPERATURE  OF  THE  EARTH  AT  ITS  SURFACE,  AS  DEPENDENT  OK 

THE  SUN. 

The  general  temperature  of  the  earth  is  doubtless  regulated  by 
its  situation  in  the  universe,  and  more  especially  by  its  position 
with  respect  to  the  sun.  To  this  position,  as  formerly  observed, 
the  properties  of  its  constituent  principles  have,  most  obviously, 
been  all  adapted  with  consummate  wisdom  ;  so  that,  under  the 
circumstances  in  which  they  are  placed,  some  are  solid,  some 
liquid,  others  gaseous,  according  to  the  purposes  they  are  intended 
to  fulfil  in  nature. 

But  the  heat  and  light  derived  from  the  sun  are  very  unequally 
distributed  over  the  surface  of  the  earth  ;  and  every  one  is  familiar 
with  the  fact,  that  as  we  recede  from  the  equator  towards  the  north 
or  south,  the  temperature  of  the  earth's  surface  gradually  dimi- 
nishes till  we  arrive  at  the  polar  regions. 

Such  is  the  general  fact.  But  the  circumstances  which  conspire 
to  interfere  with  this  gradual  distribution  of  temperature  are  so  nu- 
merous and  so  influential,  that  the  actual  temperature  of  a  place 
can  be  learnt  only  by  observation.  Among  the  circumstances  thus 
more  especially  aflecting  the  distribution  of  temperature,  may  be 
mentioned  the  nature  of  the  surface,  whether  water  or  land, — and 
the  situation,  whether  at  a  greater  or  at  a  less  height  above  the 
level  of  the  ocean.  To  these  may  be  added  the  particular  confi- 
guration and  geographical  relations  of  places  :  such  as  their  aspect 
to  the  north  or  south  ;  their  being  sheltered  or  exposed ;  the  com- 
position and  nature  of  the  soil,  such  as  its  colour  and  state  of  ag- 
gregation, on  which  depend  its  powers  of  absorbing  and  of  radiating 
heat  and  light,  and  of  retaining  or  of  parting  with  humidity,  &c. ; 
also  the  proximity  or  absence  of  seas  ;  the  predominancy  of  cer- 
tain winds  ;  the  frequency  of  clouds,  fogs,  &c.  These,  and  in- 
numerable other  circumstances,  many  of  which  will  be  pointed 
out  in  subsequent  chapters,  contribute  to  influence  the  tempera- 
tures of  particular  places,  and  to  render  them,  in  fact,  as  varied 
as  the  places  themselves. 

Nor  is  difference  of  place  the  only  cause  of  vicissitude  of  tem- 
perature ;  every  one  knows  that  at  the  same  place  the  temperature 
is  in  a  constant  state  of  change.  Hence  before  we  can  obtain  cor- 
rect notions  of  the  actual  temperature  of  any  given  place  or  period, 
certain  expedients  are  necessary  which  we  have  in  the  first  place 
to  consider. 


128  METEOROLOGY. 

Section  I. 
Of  Mean  TeniperafKre. 

If,  on  any  given  day,  we  observe  the  temperature  at  the  earth's 
surface,  at  the  commencement  of  every  one  of  the  twenty-four 
hours,  we  shall  find,  as  before  observed,  that  at  each  hour  the 
temperature  is  different;  and  we  naturally  inquire  which  of  all 
these  temperatures  is  to  be  chosen  in  preference,  as  the  one 
characteristic  of  the  day  and  place  ?  The  answer  to  this  ques- 
tion obviously  is  ;  that  temperature,  ivhatever  it  may  be,  ichich 
is  equidistant  from  the  extremes,  or,  as  it  is  usually  termed,  the 
mean  temperature  of  the  tvhole.  Now  this  mean  temperature 
may  be  obtained,  nearly,  by  adding  all  the  results  together,  and 
dividing  the  sum  by  the  number  of  observations  ;  thus  we  arrive 
at  the  mean  temperature  of  the  day,  by  adding  together  the  tem- 
peratures observed  at  different  hours  of  the  day,  and  dividing  the 
sum  by  the  number  of  icmperatures.  In  the  like  manner  by 
adding  together  the  mean  temperatures  of  every  day  of  a  week, 
or  of  a  month,  and  dividing  the  sum  by  the  number  of  days,  we 
obtain  the  mean  temperature  of  tiie  "week  or  month  ;  and  so  on, 
by  similarly  treating  the  mean  temperatures  of  the  monllis,  or  of 
any  number  of  years,  we  obtain  the  mean  temperature  of  the  year, 
at  a  given  place  :  and  it  is  to  be  observed  that  the  greater  tlie  num- 
ber of  observations  the  more  accurate  will  be  the  mean  result. 

Lastly,  it  remains  to  state  that  the  temperature  always  under- 
stood by  the  Meteorologist  (except  otherwise  expressed)  is  that 
of  the  air  near  the  surface  of  the  earth,  as  indicated  by  a  thermo- 
meter cfTectually  protected  from  radiation  and  foreign  influence  of 
every  kind.  The  temperature  as  indicated  by  a  thermometer  fully 
exposed  to  solar  radiation,  and  which  in  its  turn  is  allowed  to  ra- 
diate freely  in  the  sun's  absence,  is  altogether  a  dilTerent  thing; 
and  may  be  imagined  to  coincide  very  nearly  with  the  actual  tem- 
perature of  the  earth's  surface,  when  similarly  exposed.  The 
fluctuations  of  temperature  indicated  under  these  circumstances 
are  much  greater  than  those  of  the  air  above  noticed,  though  it  is 
probai)Ie  that  the  mean  of  the  whole  of  such  observations,  if  this 
mean  could  be  accurately  obtained,  would  differ  little  from  the 
mean  of  those  of  the  air. 


TEMPERATURE  OF  THE    POLES.  129 


Section  II. 


Of  the  actual  Distribution  of  Temperature  over  the  Globe.   Of 
Isothermal  Lines,  4'c.  Climate. 

The  reader  is  supposed  to  be  acquainted  with  the  principles  of 
the  common  division  of  the  surface  of  the  globe  into  five  zones  or 
portions,  usually  denominated  the  torrid,  the  iwo  frigid,  and  the 
two  intermediate  temperate  zones  ;  and  that  generally  speaking 
the  poles  and  the  equator  present  the  extremes  of  temperature 
upon  the  earth's  surface.  Now,  in  considering  the  general  distri- 
bution of  temperature  over  the  globe,  the  extreme  temperatures 
naturally  claim  our  attention  in  an  especial  manner :  we  shall, 
therefore,  in  the  first  place,  proceed  to  consider  the  temperature 
of  the  polar  and  of  the  equatorial  regions. 

Of  the  Tetnperature  of  the  Poles  and  of  the  polar  Regions. — 
The  probable  mean  temperature  of  the  poles  has  always  been  an 
interesting  subject  of  meteorological  inquiry.  It  must  be  confess- 
ed, however,  that  after  all  that  of  late  years  has  been  done  by 
our  enterprising  countrymen,  much  is  yet  necessary  to  enable  us 
to  arrive  at  satisfactory  conclusions.  Thus  it  has  been  shown 
that  in  attempting  to  calculate  the  tem.perature  of  the  North  Pole, 
we  shall  obtain  very  dilTerent  results  by  employing  the  tempera- 
ture occuring  in  the  old  world,  and  that  observed  in  the  new 
world  ;  the  temperature  of  the  old  world  indicating  the  temperature 
of  the  pole  to  be  about  10°;  while  the  temperature  of  the  new 
world  indicates  it  to  be  considerably  below  Zero.  Hence  it  has 
been  inferred,  that  there  are  two  points  or  poles  of  greatest  cold 
situated  in  about  the  latitude  of  80°  north,  and  in  longitudes  95° 
east,  and  100°  west ;  and  consequently  that  the  geographical  pole 
of  the  globe  is  not  the  coldest  point  of  the  iVrctic  hemisphere. 
Whether  this  deduction  be  well  founded  or  not  must  be  decided 
by  future  observation.  At  present  the  actual  temperature  of  the 
Polar  regions  cannot  be  considered  as  determined. 

Although  we  are  thus  unable  to  state  with  certainty  the  temper- 
ature of  the  Polar  regions,  it  may  nevertheless  be  deemed  an  object 
of  curiosity  to  know  the  lowest  temperatures  that  have  been  no- 
ticed. Perhaps  the  lowest  authentic  observations  of  temperature 
we  possess  are  those  by  Captain  Parry  at  Melville  Island.  Here 
the  thermometer  in  the  ship  was  often  observed  as  low  as  — 50°  ; 
and  at  a  distance  from  the  ship  even  as  low  as  55°  under  Zero. 
We  believe  still  lower  temperatures  than  these  are  on  record, 
but  probably  they  are  not  to  be  relied  on.  The  greatest  degree  of 
cold  hitherto  produced  artificially  has  been  91°  under  Zero. 


130  METEOROLOGY. 

Of  the  mean  annual  Temperature  of  the  Equator.  The  mean 
annual  temperature  of  the  equatorial,  like  that  of  the  polar  regions, 
is  a  meteorological  problem  of  considerable  interest.  Humboldt, 
from  a  very  extensive  generalization,  fixed  the  mean  equatorial 
temperature  at  8 11°  ;  and  the  same  temperature  has  been  adopted 
by  others.  Attempts,  however,  have  been  recently  made  to  show 
that  this  temperature  is  3°  or  4°  below  the  truth  ;  but  Humboldt 
in  reply  still  maintains  his  former  opinion.  Since  at  the  equator, 
only  about  one-sixth  oftlie  whole  circumference  of  the  globe  is  dry 
land,  the  general  equatorial  temperature,  as  actually  found  to  exist, 
is  perhaps  lower  than  upon  theoretical  principles  it  ought  to  be  ; 
and  cerlaiuly  much  below  what  it  ought  to  be,  as  deduced  from 
observations  made  on  the  continent  in  the  neighbourhood  of  the 
equator.  Thus  the  mean  temperature  of  Pondicherry,  in  latitude 
11°  55'  north  is  at  least  85°  ;  and  if  from  this  temperature  that  of 
the  equator  were  deduced  according  to  the  common  principles, 
the  deduction  v/ould  of  course  be  much  above  the  truth.  Tlie  fact 
is,  as  in  the  case  of  the  Polar  regions,  we  do  not  possess  the  re- 
quisite data  for  determining  the  equatorial  temperature  in  a  per- 
fectly satisfactory  manner. 

As  in  speaking  of  the  Polar  regions,  we  noticed  the  lowest 
degree  of  temperature  which  had  been  observed,  perhaps  while 
speaking  of  the  equatorial  regions  it  may  not  be  deemed  irrele- 
vant to  notice  the  highest  temperature.  Observations,  however, 
of  this  kind,  being  principally  founded  on  the  incidental  notices  of 
travellers,  are  not,  in  general,  much  to  be  relied  on;  or  are  to  be 
considered  only  as  approximations.  Thus  the  thermometer  has 
been  recorded  at  Benares  to  stand  at  110°,  113°,  and  even  118°. 
At  Sierra  Leone,  it  has  been  observed,  when  placed  on  the  ground 
to  indicate  a  temperature  of  138°.  Humboldt  also  gives  many 
instances  of  the  temperature  of  the  surface  of  the  earth,  amount- 
ing to  118°,  120°,  and  129°  ;  and  on  one  occasion  he  found  the 
temperature  of  a  loose  and  coarse  granitic  sand  to  amount  to  up- 
wards of  140°,  the  thermometer  in  the  sun  at  the  time  only  indi- 
cating a  temperature  of  about  97°. 

Of  the  Temperature  of  the  intermediate  Regions  of  the  Globe. 
Of  Isothermal  Lines,  S,'C.  With  respect  to  the  temperatures  of 
those  parts  of  the  earth  between  the  poles  and  the  equator,  it  may 
be  remarked,  that,  except  for  reference  only,  the  old  division,  be- 
fore mentioned,  of  the  earth's  surface  into  zones  is  now  almost 
entirely  superseded  by  the  more  precise  and  natural  arrangement, 
termed  tlic  Isothermal  arrangement.  According  to  this  arrange- 
ment, all  the  places  upon  the  globe  having  the  same  annual  mean 
temperature  are  classed  together  ;  and  lines  drawn  upon  a  map 
through  such  a  series  of  places,  have  been  termed  Isothermal 


ISOTHERMAL    LINES.  131 

lines,  or  lines  of  equal  temperature.  As  niig-lit  be  expected  from 
what  has  been  ah'eady  stated,  the  courses  of  these  lines  are  by  no 
means  regular.  Thus,  suppose  two  travellers  set  out,  the  one 
from  London  and  the  other  from  Paris,  and  each  visit  all  the 
places  in  the  northern  hemisphere  in  which  the  mean  annual  tem- 
peratures are  the  same  as  in  these  two  cities.  It  will  be  found 
that  the  lines  of  their  routes,  or  the  isothermal  lines  of  these  two 
cities,  will  not  only  not  follow  the  parallels  of  their  latitude,  but 
that  they  will  not  be  parallel  to  each  other  ;  and  the  same  may 
be  said  to  be  the  case  with  any  other  two  places  upon  the  globe. 
Hence,  as  the  isothermal  lines  are  as  numerous  as  the  places, 
and  as  diversified  as  numerous,  geographers  have  grouped  them 
into  bands  or  zones.  Thus  Humboldt  (to  whom  we  owe  most 
that  has  been  done  on  this  subject)  has  divided  the  northern  he- 
misphere into  the  following  six  isothermal  bands  or  zones,  viz.: 

1.  The  zone  of  mean  annual  temperature  ranging-  from  32°  to  41°. 

2.  -  -  -  -  from  41°  to  50°. 

3.  -  -  -  -  from  50°  to  59°. 

4.  -  -  -  -  from  59°  to  68°. 

5.  -  -  -  -  from  68°  to  77°. 

6.  -  -  -  -  from  77°  upv/ards. 

The  tables  given  in  the  appendix  contain  a  general  view  of  Hum- 
boldt's results.  We  shall  content  ourselves  with  briefly  pointing 
out  the  approximate  course  of  the  most  interesting  of  these  lines, 
viz.  the  Isothermal  line  of  32°. 

If  we  begin  to  trace  this  important  line  from  the  eastern  parts 
of  Siberia  in  longitude  130°  east,  we  shall  find  that  in  this  meri- 
dian it  commences  nearly  in  the  latitude  of  59°  north ;  whence 
it  makes  a  gradual  bend  northwards,  and  crosses  the  parallel  of 
60°,  nearly  in  longitude  90°.  From  this  point  it  still  advances 
to  the  northward,  and  crossing  the  arctic  circle  in  longitude  45° 
east,  arrives  at  its  most  northern  extremity  in  about  latitude  67^°, 
longitude  10°  east.  From  this  its  most  northerly  limit  our  line 
takes  a  gradual  sweep  towards  the  south,  recrosses  the  arctic 
circle  in  longitude  15°  west,  and  passing  through  the  north-west 
of  Iceland,  divides  the  parallel  of  60°  in  longitude  42°  west. 
From  this  spot  it  proceeds  southwards  to  the  latitude  of  54°,  a 
little  to  the  north  of  Table  Bay,  in  Labrador ;  gradually  de- 
clining in  its  course  till  it  arrives  at  longitude  100°  west,  in  the 
central  parts  of  the  new  continent.  Hence  the  Isothermal  line 
of  32°,  ranges  through  a  space  of  14°  or  15°  of  latitude  ;  while 
its  western  extremity,  in  the  central  parts  of  America,  is  5°  or  6° 
nearer  the  equator  than  its  eastern  extremity  in  Siberia— a  cir- 
cumstance strikingly  illustrative  of  the  greater  cold  of  the  new 


132  METEOROLOGY. 

continent  in  the  same  parallel  of  latitude.  The  most  remarkable 
circumstance  connected  with  them  is,  that  as  tlio_y  approach  the 
equator  they  gradually  become  less  convex  towards  the  north,  so 
tiiat  the  Isothermal  line  of  77°  differs  but  little  from  a  straight  line, 
coincident  with  the  tropic  of  cancer. 

In  the  arrangement  above  described  the  mean  temperatures  of 
the  whole  year  are  supposed  to  be  classed  together  ;  but  it  is  ob- 
vious that  the  same  principle  may  be  applied  to  any  portion  of 
the  year,  as  the  extreme  winter  and  summer  temperatures.  Such 
classifications  are  often,  as  we  shall  presently  see,  of  great  im- 
portance in  enabling  us  to  estimate  the  characters  of  a  particular 
country.  Thus,  lines  drawn  through  places  having  the  same 
summer  and  the  same  winter  temperatures,  are  denominated  Iso- 
theral  and  Isocheimcd  lines;  while  lines  drawn  through  places 
having  other  common  temperatures,  receive  other  appropriate 
names. 

After  these  general  remarks,  we  proceed  to  give  a  summary 
sketch  of  the  actual  distribution  of  temperature  over  the  northern 
hemisphere^  which  we  shall  subjoin  in  the  words  of  Humboldt. 
The  whole  of  Europe,"  says  this  distinguished  philosopher, 
compared  with  the  eastern  parts  of  America  and  Asia  has  an 
insular  climate  ;  and  upon  the  same  Isothermal  line  the  summers 
become  warmer,  and  the  winters  colder,  as  we  advance  from  the 
meridian  of  Mont  Blanc  towards  the  east  or  the  west.  Europe 
may  be  considered  as  the  western  prolongation  of  the  old  conti- 
nent; and  the  western  parts  of  all  continents  are  not  only  warmer 
at  equal  latitudes  than  the  eastern  parts  ;  but  even  in  the  zones 
of  equal  annual  temperature,  the  winters  are  more  rigorous,  and 
the  summers  hotter  on  the  eastern  coasts  than  on  the  western 
coasts  of  the  two  continents.  The  northern  part  of  China,  like 
the  Atlantic  region  of  the  United  States,  exhibits  seasons  strongly 
contrasted  ;  wliile  the  coasts  of  New  California  and  the  embou- 
chure of  the  Columbia  have  winters  and  summers  almost  equally 
temperate.  The  meteorological  constitution  of  those  countries  in 
the  north-west  resembles  that  of  Europe  as  far  as  50°  or  52°  of 
latitude.  In  comparing  the  two  systems  of  climates,  the  concave 
and  the  convex  summits  of  the  same  Isothermal  lines,  M^e  find  at 
New  York  the  summer  of  Rome  and  the  winter  of  Copenhagen  ; 
at  Quebec,  the  summer  of  Paris  and  the  winter  of  St.  Petersburgh. 
At  Pekin,  also,  where  the  mean  temperature  of  the  year  is  that 
of  the  coasts  of  Brittany,  the  scorching  heats  of  summer  are 
greater  than  at  Cairo,  and  the  winters  are  as  rigorous  as  at  Upsal. 
So  also  the  same  summer  temperature  prevails  at  Moscow,  in  the 
centre  of  Russia,  as  towards  the  mouths  of  tlie  Loire,  notwith- 
standing a  difference  of  11°  of  latitude  ;  a  fact  that  strikingly  illus- 


TEMPERATURE  OF  THE  N.  AND  S.  HEMISPHERES.  133 

Irates  the  effects  of  the  earth's  radiation  on  a  vast  continent 
deprived  of  mountains.  This  analogy  between  the  eastern  coasts 
of  Asia  and  America  sufliciently  proves,"  continues  Humboldt, 
"  that  the  inequalities  of  the  seasons  depend  on  tlie  prolongation 
and  enlargement  of  continents  towards  the  pole  ;  on  the  size  of 
seas  in  relation  to  their  coasts  ;  and  on  the  frequency  of  the 
north-west  winds,  and  not  on  the  proximity  of  some  plateau  or 
elevation  of  the  adjacent  lands.  Tlie  great  table  lands  of  Asia  do 
not  stretch  beyond  53°  of  latitude  ;  and  in  the  interior  of  the  new 
continent,  all  the  immense  basin  bounded  by  the  Alleghany  range, 
and  the  rocky  mountains,  is  not  more  than  from  656  to  920  feet 
above  the  level  of  the  ocean." 

The  following  remarks  apply  to  the  temperature  of  the  south- 
ern hemisphere. 

The  general  temj)eratures  of  the  northern  and  of  the  southern 
hemispheres  are  understood  to  differ  very  considerably.  This 
difference,  however,  does  not  depend  upon  any  material  difference 
in  the  proportion  of  heat  and  light  derived  from  the  sun,  as  will 
be  presently  show^n ;  but  on  the  very  unequal  distribution  of  sea 
and  of  kxnd  in  the  two  hemispheres.  The  small  quantity  of  land 
in  the  southern  hemisphere  contributes  not  only  to  equalize  the 
seasons,  but  also  to  diminish  the  annual  temperature  of  that  part 
of  the  globe  ;  and  hence  the  Polar  ice  in  the  southern  hemisphere 
advances  more  tow^ards  the  equator  than  in  the  northern  hemi- 
sphere, particularly  where  the  Antarctic  Ocean  is  free  from  land. 

Humboldt  has  shown,  that  near  the  equator,  and  indeed  so  far 
south  as  40°  or  50°,  the  correspondent  Isothermal  lines  are  in 
both  hemispheres  almost  equally  distant  from  the  poles;  and 
that,  in  considering  only  the  transatlantic  climates  between  70° 
and  80°  of  west  longitude,  the  mean  temperatures  of  the  year, 
under  corresponding  geographic  parallels,  are  even  greater  in  the 
southern  than  in  the  northern  hemisphere.  It  is  the  division  of 
heat,  therefore,  between  the  different  seasons  of  the  year,  rather 
than  the  absolute  amount  of  heat  during  the  whole  year,  that  gives 
a  particular  character  to  southern  climates,  and  approximates  them 
generally  to  the  character  of  insular  climates.  Thus,  in  the 
southern  hemisphere,  and  on  the  Isothermal  lines  46.4°  and  50° 
we  find  summers  which,  in  our  hemisphere,  belong  only  to  the 
Isothermal  lines  of  35.6°  and  40°.  The  mean  temperature  is  not 
precisely  known  beyond  51°  of  south  latitude;  yet  there  is  no 
reason  to  infer  that  the  Isothermal  line  of  32°  is  much  further 
from  the  south  pole,  than  in  the  opposite  hemisphere,  the  similar 
line  is  from  the  north  pole  ;  and  some  circumstances  at  first  sight 
appear  to  show  that  the  Isothermal  line  of  32°  is  even  nearer  to 
the  south  pole  than  it  is  to  the  north  pole  ;  though  these  circum- 
stances are  probably  deceptive.    With  respect  to  the  temperature 

12 


134  METEOROLOGY. 

of  the  south  pole  itself,  like  that  of  the  north  pole,  we  have  no 
means  of  forming  an  accurate  estimate. 

Such  is  a  summary  account  of  the  general  distribution  of  tem- 
perature over  the  northern  and  southern  hemispheres.  Now  amidst 
the  infinite  changes  every  where  going  on,  there  is  nevertheless 
at  the  same  place  a  certain  average  state  of  things  which  talven  to- 
gether, constitute  what  is  called  the  climate  of  the  place.  Of 
climate,  undoubtedly,  temperature  is  the  most  important  ingredi- 
ent. But  the  circumstances,  besides  mere  temperature,  whicii 
enter  into  the  formation  of  climate,  are  so  numerous  and  diversified, 
and  their  operation,  in  consequence,  is  so  complicated,  that  it 
becomes  exceedingly  difficult  to  unravel  and  display  them  in  a 
satisfactory  manner.  The  constituents  of  climate,  however,  ap- 
pear to  be  most  naturally  divided  into  two  great  sections  ;  viz., 
those  of  a  primary  kind  depending  vpon  the  globular  Jigiire  of 
the  earth  ;  upon  its  motion  in  its  orbit,  and  upon  its  axis :  and 
those  of  a  secondary,  or  subsidiary  kind,  more  immediately 
connected  ivith  the  globe  itself,  and  depending  upon  the  nature 
of  its  surface,  as  composed  of  Icmd  or  icater  ;  or,  as  connected 
with  its  atmosphere.  Under  these  two  points  of  view,  -we  purpose 
to  consider  the  subject  of  Climate,  in  the  following  chapters. 


CHAPTER  IV. 

OF  THE  PRIMARY  CONSTITUENTS  OF  CLIMATE  .*  OR,  OF  THE  TEMPERATURE 
OF  THE  EARTH,  AS  DEPENDENT  ON  ITS  GLOLULAR  FORM  ;  AND  ON  ITS  AN- 
NUAL AND  DIURNAL  MOTIONS. 

The  distance  of  the  earth  from  the  sun  is  such,  that  the  solar 
rays  may  be  supposed  to  arrive  at  the  earth's  surface  in  a  state  of 
parallelism.  Now,  when  parallel  rays  fall  upon  a  globe,  it  is  ob- 
vious that  any  number  of  such  rays  falling  perpendicularly,  as  at 
the  equator  of  our  earth,  will  occupy  a  very  different  portion  of 
the  surface  of  the  globe,  from  what  an  equal  number  of  the  same 
rays  will  occupy  where  they  fall  obliquely,  as  in  our  polar  regions. 
Hence,  as  we  recede  from  the  equator  towards  each  pole,  heat  and 
light  are  diflfused  over  gradually  increasing  portions  of  the  earth's 
surface,  and  thus  the  intensity  of  both  decreases  in  a  like  propor- 
tion. The  exact  law  of  such  decrease  is  well  known  to  mathema- 
ticians, but  need  not  be  here  repeated.  For  our  present  purpose 
it  is  sufhcient  to  observe,  that  among  the  natural  causes  afiecting 
the  distribution  of  heat  and  light  in  different  latitudes,  the  globular 
figure  of  the  earth  is  the  principal. 

The  second  great  natural  cause  of  the  unequal  distribution  of 


PRIMARY  CONSTITUENTS  OF  CLIMATE.  135 

heat  and  light  over  the  earth,  is  the  obliquity  of  the  earth's  motion 
in  its  orbit  with  respect  to  the  phme  ot  ils  etiualor.  From  this 
obUquity  it  happens  that,  during  the  annual  revolution  of  the  earth 
round  the  sun,  every  part  of  ils  surface,  between  the  latitudes  of 
23^°  north  and  south  from  the  equator,  is  in  turn  exposed  to  the 
perpendicular  influence  of  the  sun.  To  this  oblique  motion  of 
the  earth  in  its  orbit  we  owe  the  endless  variations  and  vicissitudes 
of  seasons  in  different  latitudes. 

There  is  also  another  circumstance  connected  with  the  earth's 
motion  in  its  orbit,  which,  as  partaking  of  the  character  of  a  pri- 
mary cause,  may  here  be  briefly  noticed.  The  earth's  orbit  is 
not  a  circle,  but  an  ellipse,  of  which  the  sun  occupies  one  of  the 
foci.  Now,  it  has  been  so  arranged,  that  in  the  middle  of  our 
winter,  the  earth  is  in  that  part  of  its  orbit  which  is  nearest  to  the 
sun.  The  earth,  therefore,  is  at  Christmas  actually  about  three 
millions  of  miles  nearer  to  the  sun  than  at  Midsummer.  Hence 
it  might  be  inferred  that  the  temperature  of  the  southern  hemi- 
sphere, which  during  our  winter  is  direcQy  exposed  to  the  sun, 
would  be  affected  by  this  greater  proximity.  Such,  however,  is 
not  the  case  ;  for  this  greater  proximity  to  the  sun  is  almost  ex- 
actly counterbalanced  by  the  swifter  motion  of  the  earth  along  this 
part  of  its  orbit.  The  eccentricity  of  the  earth's  orbit,  therefore, 
has  little  or  no  influence  on  ils  temperature  as  at  first  sight  might 
be  supposed.* 

The  third  o-reat  natural  cause  affectino^  the  distribution  of  heat 
and  light  over  the  earth  is  the  earth's  revolution  on  its  axis.  To 
this  revolving  motion  we  owe  the  innumerable  minor  vicissitudes 
of  temperature,  and  of  light  and  shade,  daily  and  hourly  experi- 
enced throughout  the  world. 

Such  are  the  three  great  natural  causes  which  regulate  the  dis- 
tribution of  heat  and  light  over  our  globe.  They  may  be  consi- 
dered as  the  nece;fsary  results  of  more  general  laws  to  which  the 
Great  Author  of  nature  has  chosen  to  restrict  himself,  and  to  which, 

*  Or,  perhaps,  to  quote  the  more  precise  explanation  of  Sir  J.  Herschel, 
"  The  momentary  supply  of  heat  received  by  the  earth  from  the  sun  varies 
in  the  exact  proportion  of  the  angular  velocity,  that  is  of  the  momentary 
increase  of  long-itude.  Hence  the  greater  proximity  of  the  sun  in  the  winter 
is  exactly  compensated  for  by  the  earth's  more  rapid  motion,  and  thus  an 
equilibrium  of  heat  is,  as  it  were,  maintained.  AVere  it  not  for  this,  the 
eccentricity  of  the  orbit  would  materially  influence  the  transition  of  the 
seasons  ;  and  the  effect  would  be  to  exaggerate  the  difference  of  summer 
and  winter  in  the  southern  hemisphere,  and  to  moderate  it  in  the  northern  j 
thus  producing  a  more  violent  alternation  of  climate  in  the  one  hemisphere, 
and  an  approach  to  perpetual  spring  in  the  other.  As  it  is,  however,  one 
such  inequality  subsists,  but  an  equal  and  Impartial  distribution  of  heat 
and  light  is  accorded  to  both."  Treatise  on  Astronomy,  p.  198,  (Lardner's 
Cyclopaedia). 


136  METEOROLOGY. 

as  usual,  He  most  rifridly  adheres.  Why,  among  the  numerous 
possible  moans  by  wliich  heat  and  light  might  have  been,  and  in 
other  instances,  are  distributed  from  a  central  sun  over  a  distant 
planet,  these  regulating  causes  have  been  selected  for  our  earth,  is 
absolutely  unknown  to  us.  That  this  selection  has  been  made 
with  some  ulterior  view  we  cannot  hesitate  to  beheve  ;  and  one 
such  view  or  purpose  may  have  been  to  demonstrate  to  us  His 
wisdom  and  His  power,  by  the  methods  cliosen  for  obviating  the 
difHculties  necessarily  resultinff  from  these  primary  arrano-ements. 
In  other  planets,  M-here  other  primary  arrangements  for  the  dis- 
tribution of  heat  and  light  have  been  adopted,  there  are  probably 
other  modes  of  obviating  the  difliculties  arisinsf  from  them.  Of 
such  arrangements  we  can  form  no  conception ;  but  to  the  inhabi- 
tants of  these  planets,  they  are  doubtless  an  equal  evidence  of  the 
wisdom  and  the  power  of  the  Deity. 


CHAPTER  V. 

OF  THE  SECONDARY  OR  SUBSIDIARY  CONSTITUENTS  OF  CLIMATE  :  COMPRE- 
HENDING A  SKETCH  OF  THOSE  CIRCUMSTANCES  CAPABLE  OF  INFLUENCING 
CLIMATE  WHICH  ARE  MORE  IMMEDIATELY  CONNECTED  WITH  THE  SUR- 
FACE OF  THE  GLOBE,  AS  CONSISTING  OF  LAND  OR  WATER  ;  OR  W^HICH  ARE 
CONNECTED  WITH  THE  ATMOSPHERE. 

In  the  preceding  chapter  we  have  alluded  to  the  difhculties  or 
exigencies  necessarily  arising  from  tlie  modes  in  which  heat  and 
light  are  distributed  over  our  globe  ;  and  of  these,  before  we  pro- 
ceed, it  may  be  proper  to  specify  some  of  the  most  striking. 

Had  the  heat  and  liofht  derived  from  the  sun  to  the  earth  not 
been  in  any  way  moditied,  the  equatorial  and  the  polar  regions 
would  have  been  alike  inaccessible  to  organic  life.  The  heat  with- 
in the  tropics  and  the  cold  towards  the  poles,  would  both  have  been 
destructive  ;  while  the  intermediate  regions  would  have  been  ex- 
posed to  a  constant  succession  of  violent  and  sudden  alternations 
of  temperature,  that  would  have  rendered  the  present  state  of  things 
no  less  an  impossibility.  In  order,  therefore,  to  render  this  earth 
an  appropriate  dwelling-place  for  such  beings  as  at  present  occupy 
its  surface,  it  was  necessary  that  these  extremes  and  sudden  vicis- 
situdes of  temperature  should  be  in  some  way  diminished  and  al- 
leviated. Accordingly  these  objects  have  been  effected  with  the 
most  consummate  wisdom.  Indeed,  some  of  the  most  splendid 
instances  of  design  in  nature  are  offered  by  those  subsidiary 
arrangements,  by  which  the  difficulties  necessarily  arising  from 
the  primary  arrangements  are  obviated  or  mitigated;  and  by 
which  the  greater  portion  of  the  earth's  surface  has  been  made  ac- 


SECONDARY  CONSTITUENTS  OF  CLIMATE.  137 

cessible  to  organic  beings  of  the  same  general  character.  These 
subsidiary  arrangements  it  will  be  our  business  to  explain  in  the 
present  chapter. 

The  secondary  or  subsidiary  constituents  of  climate  naturally 
divide  themselves  into  two  great  sections;  viz.,  those  connected 
with  the  surface  of  the  globe,  as  composed  of  land  or  water ; 
and  those  connected  ivith  the  atmosphere. 

In  the  following  sketch  of  these  constituents  of  climate  we  have 
endeavoured  as  usual  to  elucidate  principles  rather  than  to  enter 
into  details  ;  and,  as  far  as  is  compatible  with  a  general  and  popular 
view,  have  attempted  to  point  out  the  m.odes  in  which  the  laws  of 
light  and  heat,  described  in  the  first  Book,  operate,  so  as  to  pro- 
duce the  phenomena  of  climate. 


Section  I. 

Of  the  secondary  Constituents  of  Climate,  immediately  connected 
with  the  Surface  of  the  Globe  ;  and  depending  on  the  Nature 
of  that  Surface  as  composed  of  Land  or  PFater. 

In  attempting  to  illustrate  the  operation  of  the  laws  of  heat  and 
light  in  the  formation  of  climate,  we  shall  follow  the  order  nearly 
in  which  these  laws  were  discussed  in  the  previous  chapters  ;  that 
is  to  say,  we  shall  first  consider  the  influence  of  heat  and  light  as 
depending  on  their  latent  and  decomposed  forms  ;  and  afterwards 
their  influence  as  depending  on  their  radiation,  conduction,  and 
convection. 

In  the  prosecution  of  this  difficult  inquiry,  the  first  circumstance 
which  naturally  claims  our  attention,  is  the  absolute  quantity  of 
heat  and  light  derived  from  the  sun  to  the  earth. 

I.  Of  the  Proportion  of  Solar  Heat  and  Light  that  actually 
arrives  at  the  Surface  of  the  Earth.  Of  the  absolute  quantity  of 
heat  and  light  derived  from  the  sun  to  our  globe  we  have  no  means 
of  forming  an  exact  estimate.  M.  Pouillethas  attempted  to  show 
that  the  amount  of  heat  annually  received  by  the  earth  from  the 
sun,  is  equal  to  that  which  w^ould  be  required  to  melt  a  stratum 
of  ice  nearly  forty-six  feet  thick,  and  covering  its  whole  surface.* 
This  estimate,  however,  is  to  be  viewed  only  as  a  rude  approxi- 
mation. The  difficulty  lies  not  only  in  the  impracticability  of  form-" 
ing  precise  notions  of  the  heat  and  light,  which  actually  arrive  at 
any  given  place  in  a  given  time  ;  but  in  the  utter  impossibility  of 
forming  even  a  conjecture  of  those  portions,  which  become  latent 
or  are  otherwise  lost  in  the  passage  of  the  solar  rays  through  the 

*  Elemens  de  Physique  experimentale  etde  Meteorologie,  torn.  ii.  p.  704, 

13  * 


138  METEOROLOGY. 

atmosphere.  The  following  observations  will  give  some  idea  of 
the  absolute  quantity  of  liglit  which  reaches  the  earth;  but  it  is 
proper  to  apprize  the  reader,  that  the  results  stated  are  to  be  con- 
sidered as  liable  to  much  uncertainty.  Nor  do  we  know  whether 
they  are  equally  applicable  to  heat,  which,  though  it  obeys  laws 
somewhat  analogous  to  those  of  light,  may  nevertheless  have  its 
own  peculiar  laws. 

A  vertical  ray  of  light,  in  its  passage  through  the  clearest  air,  has 
been  calculated  to  lose  at  least  a  fifth  part  of  its  intensity  before  it 
reaches  the  earth's  surface.  From  this  cause,  and  from  the  actual 
condition  of  the  atmosphere,  it  has  been  estimated  that  under  the 
most  favourable  circumstances,  of  a  thousand  rays  emanating  from 
the  sun,  only  378  on  a  medium,  can  penetrate  to  the  surface  of 
the  earth  at  the  equator,  228  at  the  latitude  of  45°,  and  110  at  the 
poles  ;  while  in  cloudy  weather  these  several  proportions  are  a 
great  deal  less.-^ 

At  present,  our  attention  is  solely  directed  to  those  portions  of 
heat  and  light  which  thus  make  their  way  to  the  earth's  surface. 
On  those  portions  retained  in  the  atmosphere  we  shall  offer  a  few 
remarks  hereafter. 

2.  Of  the  Distribution  of  Heat  and  Light  over  the  Earth''s 
Surface  in  the  latent  and  decomposed  Forms.  The  distribution 
of  heat  and  light  in  the  latent  state  over  the  surface  of  the  globe, 
probably  follows  laws  nearly  similar  to  those  of  the  distribution 
of  sensible  heat  and  light  formerly  mentioned;  that  is  to  say,  the 
quantity  latent,  like  the  quantity  sensible,  diminishes  from  the 
equator  toward  the  poles.  On  tTiis  subject,  however,  we  want 
the  necessary  data,  even  for  forming  an  opinion,  much  less  for  de- 
termining the  amount  and  the  exact  law  of  distribution  ;  all  of 
which  must  be  left  for  future  inquirers.  But  of  the  infinite  im- 
portance of  the  latency  of  heat,  in  the  economy  of  nature,  the  fol- 
lowing brief  remarks  will  serve  to  convey  some  notion. 

Let  us  take  the  familiar  instance  of  water,  than  by  which  im- 
portant fluid,  the  influence  of  the  latency  of  heat  cannot  perhaps 
be  more  strikingly  exemplified.  We  formerly  showed  that  the 
temperature  of  water  in  becoming  solid  on  the  one  hand,  and  ga- 
seous on  the  other,  makes,  as  it  were,  a  pause  ;  and  that  these 
changes  never  take  place  abruptly.  The  consequence  of  this  ar- 
rangement is,  that  ice  and  vapour  are  formed  slowly  and  gradu- 
ally, and  as  slowly  and  gradually  again  become  water  ;  while 
sudden  transitions  from  one  state  to  the  other  are  thus  entirely  pre- 
vented. Were  it  not  for  this  beautiful  provision,  we  should  be 
constantly  liable  to  inundations,  and  other  inconveniences,  that 
would  absolutely  have  rendered  the  world  uninlrabitable.     It  is 

•  Article  Climate  in  the  Encyclopaedia  Britannica. 


DISTRIBUTION  OF  ELECTRICITY  AND  MAGNETISM.  139 

impossible,  therefore,  to  reflect  upon  the  arrangement  itself,  or 
upon  the  means  by  which  it  has  been  effected,  without  being  im- 
pressed with  the  most  profound  admiration,  not  only  of  the  wis- 
dom of  the  Great  Designer  of  the  whole,  but  of  his  goodness  and 
benevolence. 

The  distribution  of  heat  and  light  in  the  decoinposed  forms,  like 
the  other  conditions  of  these  great  principles,  decreases  from  the 
equator  towards  the  poles.  We  formerly  alluded  to  the  opinion 
that  heat,  whatever  it  may  consist  of  besides,  appears  occasionally 
to  be  convertible  into  the  electric  and  magnetic  energies.  This 
conversion,  under  certain  circumstances,  may  be  true  of  sensible 
heat ;  but  heat,  in  the  latent  or  combined  form,  is  perhaps  most 
liable  to  be  so  converted.  Without  pretending  to  offer  any  opi- 
nion, one  way  or  the  other,  on  this  view  of  the  nature  of  heat,  we 
shall,  nevertheless,  adopt  it  for  the  sake  of  convenience,  and  shall, 
therefore,  next  consider  the  subject. 

Of  the  Cicnercd  Distribution  of  Electricity  and  Magnetism 
over  the  Earth.  The  recent  discoveries  on  the  connection  of  elec- 
tricity and  magnetism,  formerly  described,  have  thrown  much  light 
on  the  distribution  of  these  important  agencies  over  the  globe  ;  and 
the  present  extent  of  our  knowledge  regarding  them  will  be  un- 
derstood by  the  general  reader  from  the  following  summary. 

Every  one  is  familiar  with  the  ordinary  phenomena  of  a  mag- 
netic needle  freely  suspended,  and  with  its  tendency  to  assume  a 
position  more  or  less  approaching  to  parallelism  to  the  earth's 
axis  ;  that  is  to  say,  that  all  over  the  world  it  points  nearly  north 
and  south.  Most  persons,  probably,  are  also  acquainted  with  the 
phenomenon  termed  the  dip  or  inclination  of  the  magnetic  needle : 
thus,  in  the  latitude  of  London,  a  needle  exactly  poised  and  freely 
suspended,  instead  of  assuming  a  horizontal  position,  will  settle 
at  an  angle  of  70°,  the  north  pole  being  downwards.  If  we  carry 
such  a  needle  southwards,  towards  the  equator,  we  observe  that 
the  dip  gradually  diminishes  ;  till  at  a  certain  point,  nearly  coin- 
ciding with  the  earth's  equator,  it  has  no  dip  at  all,  but  assumes  a 
perfectly  horizontal  position.  A.s  we  still  proceed  towards  the 
south,  the  dip  again  makes  its  appearance,  but  in  an  opposite  di- 
rection, the  soutli  pole  being  now  next  the  earth's  surface.  To 
understand  the  reason  of  this  dip  of  the  magnetic  needle  and  of 
its  general  direction,  we  have  only  to  consider  that  the  earth  itself 
is  a  magnet,  the  poles  of  which  are  situated  beneath  its  surface. 
The  directive  property  of  the  needle  is  owing  to  these  poles  ;  and 
when  the  needle  is  on  the  north  side  of  the  equator,  the  north 
pole  of  the  earth  having  the  greatest  effect,  the  needle  is  attracted 
downwards,  towards  the  north  pole ;  hence,  exactly  over  the  pole 
the  needle  would  be  vertical.  Similar  phenomena  happen  in  the 
southern  hemisphere  ;  but  here  the  south  pole  predominates,  and. 


140  METEOROLOGY. 

of  course,  depresses  the  corresponding  pole  of  the  needle  ;  while, 
at  the  magnetic  equator,  from  the  equal  action  of  both  poles,  the 
needle  will  assume  an  exactly  horizontal  position.  It  may  be  re- 
marked, that  neither  the  magnetic  poles  nor  the  magnetic  equator 
coincide  exactly  with  those  of  the  earth;  and  that  this  non-coin- 
cidence is  owing  to,  or  rather  constitutes,  wliat  is  termed  the 
variation  of  the  needle ;  which  is  not  only  different  in  different 
parts  of  the  world,  but  appears  to  be  liable  to  periodical  differences 
in  the  same  place,  at  present  not  well  understood.  Such  are  the 
principal  phenomena  of  the  magnetic  needle  as  demonstrative  of 
the  earth's  magnetism,  and  which  we  shall  now  attempt  to  illus- 
trate a  little  further. 

We  have  mentioned,  that  the  earth  may  be  considered  as  a 
great  magnet.  Now,  we  have  formerly  shown  that  when  a  mag- 
netic needle  is  in  its  natural  position  of  north  and  south,  there 
exist  electri^tal  currents  in  planes  at  right  angles  to  the  needle, 
descending  on  its  east  side,  passing  under  it  from  east  to  west, 
and  ascending  on  its  west  side.  Hence,  we  must  suppose  cur- 
rents of  electricity  to  circulate  within  the  earth,  more  especially 
near  its  surface,  and  to  be  constantly  passing  from  east  to  west, 
in  planes  parallel  to  the  magnetic  equator  ;  which  electrical  cur- 
rents, if  such  can  be  demonstrated  to  exist,  will  in  their  turn  com- 
pletely account  for  the  magnetic  directive  property  of  the  earth. 
The  next  question  is,  therefore,  how  far  we  are  justified  in  as- 
suminfif  the  existence  of  such  electric  currents  within  the  earth  ? 

We  have  already  alluded  to  the  opinion  that  heat  occasionally 
passes  into  the  electric  and  magnetic  energies  ;  an  opinion  which 
some  consider  to  derive  much  probability  from  the  phenomena  of 
what  has  been  termed  thermo-electricity  ;  that  is  to  say,  electri- 
city (and  magnetism)  developed  by  the  unequal  distribution  of 
heat  through  bodies.  Now,  whether  the  phenomena  of  thermo- 
electricity actually  depend  on  the  decomposition  of  heat,  latent  or 
sensible,  or  upon  any  other  cause,  is  of  little  importance;  the 
phenomena  tliemselves  are  well  established,  and  they  seem  to 
account,  in  the  most  satisfactory  manner,  for  the  general  distri- 
bution of  electricity  and  magnetism  over  the  earth.  The  explana- 
tion is  this  :  the  earth  during  its  diurnal  motion  on  its  axis  from 
west  to  east,  has  its  surface  successively  exposed  to  the  solar  rays 
in  an  opposite  direction,  or  from  east  to  west.  The  surface  of  the 
earth,  therefore,  particularly  between  the  tropics,  will  be  heated 
and  cooled  in  succession,  from  east  to  west,  and  currents  of  elec- 
tricity, on  thermo-electric  principles,  will  at  the  same  time  be 
established  in  the  same  direction  :  now  these  currents  once  esta- 
blished from  east  to  west,  will,  of  course,  give  occasion  to  the 
magnetism  of  the  earth  from  north  to  south.  Hence  the  magnetic 
directive  power  of  the  earth,  in  a  direction  nearly  parallel  with  its 
axis,  is  derived  from   the  thermo-electric  currents,  induced  in  its 


DISTRIBUTION  OF  COLOURS.  141 

equatorial  regions  by  the  unequal  distribution  of  heat  there  pre- 
sent, and  depending  principally  on  its  diurnal  motion. 

These  recent  and  beautiful  discoveries  show,  in  the  most 
striking  manner,  that  the  operations  of  nature  are  more  extraor- 
dinary, and  indicate  more  of  simplicity  and  wisdom  of  design  in 
proportion  as  they  are  better  understood.  By  what  simple  expe- 
dients, when  known,  are  those  wonderful  phenomena  of  the 
earth's  electricity  and  magnetism  produced,  which  formerly  ap- 
peared so  anomalous  and  perplexing  !  And  what  encouragement 
do  these  discoveries  hold  out  to  us,  with  respect  to  future  disco- 
veries, that  may  throw  still  further  light  upon  the  operations  of 
the  Great  Architect  of  the  universe. 

Of  the  Distribution  of  Light  in  the  decomposed  Form  over 
the  Globe.  Every  one  is  familiar  with  the  general  fact,  that  the 
most  splendid  exhibitions  of  colours  of  every  description  are  dis- 
played in  the  warmer  climates  ;  and  that  the  tints  of  natural  objects, 
generally  speaking,  become  more  sad  and  faded  as  we  approach  the 
colder  regions,  till  they  merge  into  the  white  of  the  polar  snows. 
Most  persons,  also,  are  aware  of  the  well  known  circumstances 
attending  the  total  abstraction  of  light  from  plants  and  animals, 
and  that  they  thus  become  more  or  less  white  or  etiolated. 
Hence,  we  need  scarcely  do  more  than  remind  the  reader,  of 
what  must  be  already  familiar  to  him,  viz.,  that  the  decided 
colours  of  tropical  productions  of  every  kind,  whether  we  con- 
sider the  gaudy  plmnage  of  the  birds,  of  the  variegated  adornment 
of  the  fishes  and  insects,  &;c.,  are  so  striking,  as  to  be  quite  cha- 
racteristic of  these  productions.  In  the  higher  latitudes,  also, 
where  the  contrast  between  the  summer  and  winter  seasons  is 
very  great,  the  colours  of  some  animals  vary  with  the  seasons  ; 
being  in  the  summer  generally  of  some  dark  hue,  but  in  the 
winter  nearly  white  ;  while  still  further,  in  the  polar  regions 
all  is  more  or  less  white,  and  the  natural  covering  of  the  earth, 
the  snow,  is  the  whitest  body  in  nature.  Putting  out  of  sight 
the  great  importance  of  the  colours  of  objects,  which  will  fall 
more  naturally  to  be  spoken  of  hereafter ;  it  may  be  remarked 
here,  that  colours  have  usually  been  considered  as  offering  to 
us  one  of  the  most  striking  instances  of  the  benevolence  of  the 
Deity.  Colours  are  universally  agreeable  to  mankind  ;  and 
the  most  incurious  and  ignorant  are  attracted  by,  and  delighted 
with,  sliowy  exhibitions  of  them.  Now,  all  this  pleasure  is 
the  gratuitous  git't  of  the  Creator,  and  places  his  benevolence  in 
the  strongest  possible  point  of  view.  There  was  no  reason  why 
man  should  have  distinguished  colours  at  all,  much  less  have 
been  delighted  witli  them  :  but  what  is  the  fact?  not  only  are  we 
gifted  with  organs  exquisitely  sensible  to  the  beauty  of  colours  ; 
but,  as  if  solely  to  gratify  this  feeling,  the  whole  of  nature,  from 


142  METEOROLOGY. 

the  liighest  to  the  lowest  of  her  productions,  forms  one  gorgeously- 
coloured  picture,  in  which  every  possible  tint  is  contrasted  or  as- 
sociated in  every  possible  manner.  Is  there  a  iiuman  being  who 
can  witness  the  splendid  colouring  of  the  atmosphere  above  him  by 
the  setting  sun  ;  who  can  witness  the  beauty  and  endless  variety 
of  tint  displayed  by  every  object  of  the  landscape  around  him, 
down  to  the  minutest  insect  or  flower  or  pebble  at  his  feet  ;  who 
is  conscious  of  the  pleasure  he  derives  from  these  objects,  and 
who  reflects  that  this  pleasure  was  not  necessary  to  his  existence, 
and  might  have  been  withheld  ?  Is  there  we  ask,  a  hum.an  being 
who  duly  considers  all  these  things,  and  who  \v\\\  dare  to  assert 
that  the  Beins:  who  made  them  all  is  not  benevolent? 

3.  Of  the  Laws  of  Absorption^  Radiation,  and  Reflection  of 
Heat  and  Light. — These  laws  as  applied  to  the  earth  generally, 
are  at  present  but  very  imperfectly  understood.  The  following 
remarks  will  serve  to  convey  some  idea  of  the  little  we  know  on 
the  subject. 

The  reader  will  bear  in  mind  what  was  formerly  stated,  that 
the  absorbing  power  of  bodies  with  respect  to  heat  (and  per- 
haps light  also)  is  directly  as  their  radiating  power,  and  inversely 
as  their  reflecting  power.  Such  is  the  general  opinion  ;  and,  as 
far  as  solar  heat  and  light  are  concerned,  this  opinion  appears  to 
be  well  founded  ;  but  we  shall  see  presently  that  there  are  strong 
reasons  for  suspecting  that  the  radiating  power  does  not  always 
follow  the  same  law  as  the  absorbing  power.  In  the  mean  time, 
however,  we  shall  proceed  to  state  what  has  been  advanced  on 
these  points. 

Mr.  Daniell  has  attempted  to  show  that  the  absorption  and  ra- 
diation of  solar  heat  increase  as  we  proceed  from  the  equator  to- 
ward the  poles.  Thus,  in  a  tropical  climate,  and  under  a  vertical 
sun,  the  greatest  extent  of  the  difference  between  two  thermome- 
ters, the  one  covered  with  black  wool,  and  exposed  to  the  direct 
rays  of  the  sun,  in  order  that  it  may  absorb  to  the  utmost  the  in- 
cident heat,  and  the  other,  uncovered  in  the  shade,  is  no  more 
than  about  47°  ;  while  two  thermometers,  similarly  circumstanced, 
in  the  middle  of  summer,  in  London,  give  a  difference  of  G5°  ; 
and  in  the  Arctic  regions  the  diflerence  often  amounts  to  90°  at 
least:  so  that  in  the  Arctic  regions  there  is  twice  as  much  heat 
and  \\^\\i  absorbed  under  similar  circumstances,  as  there  is  in  the 
tropical  regions.  The  same  gentleman  has  also  attempted  to 
show  (what  might  have  been  inferred  indeed  from  the  assumed 
relation  between  the  absorption  and  radiation  of  heat  and  light 
above  mentioned),  that  that  the  radiation  of  iieat  from  the  errlh's 
surface  obeys  similar  laws  ;  that  is  to  say,  that  the  quantity  radi- 
ated from  the  earth  increases  from  the  equator  toward  the  poles. 
Laws  somewhat  analogous,  and  which,  when  they^  are  better  un- 


ABSORPTION,  ETC.  OF  HEAT  AND  LIGHT.  143 

ilerstood,  will  probably  throw  much  information  upon  these  phe- 
nomena, seem  to  hold  with  respect  to  light.  Thus  we  formerly 
menticned  tliat  when  a  ray  of  light  falls  upon  fluids,  transparent 
bodies,  or  metals,  the  quantity  reflected  increases  with  the  angle 
of  incidence  reckoned  from  the  perpendicular;  while  the  quantity 
absorbed  of  course  decreases  in  the  same  proportion  :  but  that  on  the 
contrary  when  a  ray  falls  upon  ivhite  opaque  bodies,  the  quantity 
reflected  decreases  as  the  angle  of  incidence  increases  ;  while,  of 
course,  the  quantity  absorbed,  increases  in  the  like  proportion. 
Hence  if  heat  follows  the  same  law,  it  is  evident  that  the  quantity 
of  heat  absorbed  by  the  earth  from  the  solar  rays,  must  increase 
from  the  equator  towards  the  poles;  that  is  to  say,  as  the  angle 
of  their  incidence  increases,  as  Mr.  Daniell  has  attempted  to  show. 
It  is  proper,  however,  to  observe  that  Mr.  Daniell's  views  have 
been  called  in  question,  and  that  some  late  observations  made  in 
liiffh  latitudes  do  not  entirely  corroborate  them.*  We  have  al- 
luded  to  the  subject  merely  with  the  view  of  drawing  the  atten- 
tion of  Meteorologists  to  it  as  one  of  great  interest  and  curiosity, 
and  as  one  by  no  means  at  present  understood.  There  is  every 
reason  to  believe  that  the  absorption  (and  perhaps  the  radiation) 
of  heat  and  light,  under  some  of  its  modifications,  are  much  in- 
fluenced  by  polarization,  and  consequently  by  certain  angles  of 
incidence  and  reflection  ;  and  that  diese  circumstances,  in  conse- 
quence, have  much  to  do  with  the  distribution  of  heat  and  light, 
particularly  in  the  higher  latitudes,  where  they  may  exert  no 
small  influence  upon  organized  beings.  The  above  observations 
seem  to  point  to  the  existence  of  certain  general  laws,  which  no 
doubt  hereafter  will  be  elucidated. 

In  noticing  the  influence  of  different  colours  on  the  absorption 
and  reflection  of  heat  and  light,  we  stated  that  black  and  dark 
colours  generally  absorb  most  and  reflect  least ;  and  vice  versa, 
that  white  and  li^ht  colours,  reflect  most  and  absorb  least ;  and 
we  are  now  come  to  illustrate  this  interesting  subject,  and  to  con- 
sider the  following  questions. — Why  does  whiteness  prevail  in 
the  Polar  regions  ?  Why,  for  instance,  is  snovv  white  ?  On  the 
contrary,  why  are  all  sorts  of  dark  and  decided  colours  met  with 
in  the  tropical  climates,  except  whiteness,  which  is  comparatively 
rare?     Might  not  snow  have  been  black  instead  of  white;   which 

*  We  allude  here  to  the  observations  made  in  those  regions,  and  given 
in  the  appendix  to  Captain  Franklin's  Second  Journey,  by  Dr.  Richard- 
son, Captain  Back,  and  Lieutenant  Kendal.  In  these  observations  Dr.  R. 
states  that  the  radiation  was  much  stronger  in  the  spring  months,  ivhen 
the  ground  was  covered  with  snow,  than  in  the  summer  months,  when  the 
altitude  of  the  sun  was  greatest.  Dr.  R.  ascribes  this  greater  radiation 
to  the  greater  clearness  of  the  air  at  these  seasons,  but  were  there  no 
other  reasons  ? 


144  METEOROLOGY. 

was  just  as  likely  if  its  colour  had  been  the  result  of  accident  ? 
or  might  not  wliiieness  have  been  predominant  under  the  equator? 
Perhaps  the  best  mode  of  answering  these  questions,  and  of 
placing  the  subject  in  a  striking  view,  is  to  examine  what  would 
have  been  the  consequence,  if  whiteness  had  prevailed  under  the 
equator,  and  blackness  at  the  poles. 

As  heat  and  light  are  supposed  to  obey  nearly  the  same  laws, 
as  far  as  absorption,  radiation,  and  reileclion  arc  concerned,  it  is 
obvious  that  if  white  had  prevailed  in  the  tropical  climates,  almost 
all  the  solar  lieat  and  light,  instead  of  being  absorbed,  would  have 
been  reflected.  The  consequence  of  this  refleclion  would  have 
been,  that  the  accumulation  of  heat  and  the  glare  of  light  in  the 
lower  regions  of  the  atmosphere,  near  the  surface  of  the  earth, 
would  have  been  intolerable,  and  would  have  rendered  these  re- 
gions quite  uninlia])itable,  at  least  by  the  present  race  of  beings. 
The  surface  of  the  earth,  also,  though  it  would  have  been  heated 
slowly,  would  have  been  overlieated  in  time  ;  and  at  length  would 
probably  have  become  so  very  hot,  from  its  comparatively  low  radi- 
ating powers,  tliat  the  heat  could  not  have  been  borne.  As  it  is,  the 
heat  and  light  of  the  sun  are  absorbed  readily,  and  as  freely  given 
off*  again  by  radiation  ;  or  perhaps  the  heat,  like  the  light,  is  de- 
composed ;  and  thus  the  whole  is  preserved  in  that  comparatively 
moderate  and  nicely  balanced  state,  which  renders  even  the  hot- 
test parts  of  the  earth  inhabitable. 

On  the  other  hand  let  us  consider  for  a  moment  v/hat  would 
have  been  the  consequences  if  snow  had  been  black,  or  in  other 
words,  if  blackness  had  prevailed  in  the  Polar  regions.  In  this 
case,  all  the  little  light  and  heat  that  reach  tliem  would  have  been 
absorbed,  and  the  effect  would  have  been  darkness,  more  or  less 
complete.  From  the  rapid  melting  also  of  the  snow  on  the  least 
exposure  to  heat  and  light,  we  should  have  been  constantly  liable 
to  inundations.  Thus  the  whole  of  the  Polar  regions  of  the  earth 
would  have  been  one  dark  and  dreary  void,  inaccessible  to  organic 
life.  But  by  the  present  arrangement,  all  these  consequences 
are  obviated.  The  white  snow  absorbs  a  certain  portion  of  light 
and  of  heat  (by  a  beautiful  provision  more  as  the  angle  of  inci- 
dence increases  ?)  while  so  much  light  is  reflected  as  is  useful, 
and  no  more.*     Thus  the  adjustment  of  the  colours  of  bodies  to 

*  The  reader  will  observe  that,  under  ordinary  circumstances,  ivhite 
reflects  most  and  of  course  absoi-bs  and  radiates  least  solar  heat  and  fig-ht ; 
but  if  the  above  remarks  on  lig-lit  be  well-founded,  the  absorption  of  light 
(and  heat  i*)  by  white  bodies  increases  with  the  angle  of  inciclence.  Now, 
as  nothing  of  this  sort  is  known,  or  can  be  well  conceived  to  happen,  with 
respect  to  radiation,  the  doubt  expressed  at  the  beginning  of  this  section 
arises,  viz.,  whether  under  all  circumstances,  the  radiating  and  absorbing 
powers  of  bodies  obey  similar  laws,  even  as  far  as  the  solar  rays  are  con- 


PROPAGATION  OF  HEAT  BY  LAND.  145 

tlie  circumstances  in  which  they  are  placed,  constitutes  an  exam- 
ple of  tlie  expedients  hy  which  those  minor  inconj^ruities  are  ob- 
viated, that  are  necessarily  incidental  to  the  modes  in  which  heat 
and  light  are  distributed  over  the  globe  ;  and  presents  altogether 
one  of  the  most  obvious  and  beautiful  instances  of  design  connected 
with  the  agency  of  heat  and  light. 

Lastly,  it  may  be  worth  while  to  draw  the  attention  of  the 
reader  to  the  strikingcontrast  displayed  between  the  ponderable  and 
imponderable  forms  of  matter,  as  to  the  ease  with  which  they  are 
decomposed,  and  the  modes  in  which  they  exist  in  nature. 

We  have  seen  that  to  preserve  the  homogeneity  and  integrity 
of  ponderable  bodies,  as  of  water  and  air,  elaborate  arrangements 
have  been  adopted,  evincing  the  most  extraordinary  design  and 
wisdom  ;  because  the  decomposition  or  derangement  of  water  and 
air  would  at  once  prove  destructive  to  organized  beings.  But,  to 
preserve  the  homogeneity  of  heat,  and  particularly  of  light,  no 
such  care  is  shown,  because  no  such  care  was  particularly  neces- 
sary. The  decompositions  of  these  agencies,  therefore,  are  per- 
mitted to  take  their  natural  course;  and  by  an  admirable  provi- 
sion, so  far  are  colours,  magnetism,  Sic.  from  being  injurious  to 
us,  that  they  constitute  one  of  the  chief  sources  of  our  knowledge 
and  happiness  ! 

4.  Of  the  Conduction  of  Heat  below  the  Earth'' s  Surface  on 
Land,  The  soil,  from  a  few  inches  to  a  foot  or  more  below  the  sur- 
face, participates  very  much  in  the  fluctuations  of  the  surface  tem- 
perature. In  general,  perhaps,  it  may  be  stated,  that  the  temperature 
of  the  surface  of  the  eartli  is  a  little  above  that  of  the  incumbent  at- 
mosphere by  day,  and  below  it  by  night  ;  though  much  will  de- 
pend in  this  respect  upon  the  nature  of  the  soil,  on  its  radiating 
and  conducting  powers,  and  on  a  multiplicity  of  other  conditions 
that  will  readily  occur  to  the  reader.  At  a  certain  distance,  how- 
ever, below  the  surface,  and  varying  with  tiie  latitude  and  other 
circumstances,  there  must  be  a  determinate  stratum,  where  the 
temperature  is  uniform,  or  nearly  so,  throughout  the  year.  Ex- 
periments on  this  subject  are  very  limited  ;  but  there  is  reason  to 
believe,  that  tlie  temperature  of  this  invariable  stratum  coincides 
nearly,  with  the  mean  annual  temperature  of  the  place  ;  and  that 
its  depth  below  the  surface,  in  different  latitudes,  varies  between 
forty  and  eighty  feet.  The  reader  need  scarcely  be  reminded, 
that  the  well  known  uniformity  of  the  temperature  of  cellars  and 

cerned.  The  absorption  and  radiation  of  heat  of  low  intensity,  and  un- 
accompanied by  lig"lit,  seem  to  depend  more  upon  tiie  nature  of  the  sur- 
face than  upon  colour.  It  must  be  admitted,  however,  that  at  present  a 
great  deal  of  obscurity  hang's  over  the  whole  of  this  subject. 

13 


146  METEOROLOGY. 

caves,  depends  chiefly  upon  the  circumstances  we  are  now  con- 
sidering. As  an  instance  of  the  uniformity  of  temperature  in 
such  places,  it  may  he  mentioned,  that  a  thermometer  placed  in 
the  caves  under  the  observatory  in  Paris,  at  a  depth  of  about 
eighty-five  feet  below  the  surface,  has,  during  fifty  years,  scarcely 
varied  more  than  a  quarter  of  a  degree  from  1  r82°  of  the  centi- 
grade scale  ;  equal  very  nearly  to  53|°  of  Fahrenheit. 

A  few  experiments  have  been  made  to  determine  the  variation 
of  the  temperature,  throughout  the  year  at  different  depths  from 
the  surface,  dov/n  to  the  invariable  stratum  ;  and  the  following  is 
a  summary  of  the  results,  which,  perhaps,  may  be  considered  as 
generally  applicable  to  the  northern  hemisphere. 

In  the  month  of  August  the  temperature  of  the  ear'h  goes  on 
decreasing  in  nearly  a  uniform  manner,  from  a  little  below  the 
surface  to  tlie  stratum  of  invariable  temperature.  In  the  month 
of  September  the  temperature  is  nearly  uniform  to  fifteen  or 
twenty  feet  below  the  surface  ;  beyond  which  depth  the  temper- 
ature decreases  a  little  and  slowly  to  the  stratum  of  invariable 
temperature.  During  the  months  of  October  and  November  the 
temperature  increases  from  the  surface  to  the  depth  of  fifteen  or 
twenty  feet ;  and  below  this  point  it  remains  nearly  uniform  to 
the  invariable  stratum.  During  December,  January,  and  Feb- 
ruary, the  temperature,  being  at  its  minimum  upon  the  surface, 
increases  in  a  manner  nearly  uniform,  downwards  to  the  invaria- 
ble stratum.  During  March  and  April  there  is  a  rapid  decrease 
of  temperature  to  the  depth  of  one  or  two  feet ;  below  this  depth 
the  temperature  decreases  less  rapidly  ;  and  still  lower,  the  tem- 
perature increases  a  little.  During  the  months  of  May,  June, 
and  July,  the  temperature  being  at  its  maximum,  at  the  surface, 
decreases  downwards,  but  less  rapidly  and  to  a  greater  depth  ;  it 
then  begins  to  increase  a  little  till  it  attains  the  temperature  of  the 
invariable  stratum.  The  rapidity  and  degree,  however,  with 
which  these  changes  lake  place,  as  well  as  the  changes  themselves, 
appear  to  fluctuate  very  considerably  not  only  in  diflerent  places 
under  the  same  Isothermal  line,  but  in  the  same  place  in  different 
seasons. 

Since  heat  is  propagated  through  the  soil  by  conduction,  of 
course  it  is  propagated  in  all  directions.  Hence,  it  may  be  sup- 
posed to  move  laterally  as  well  as  downwards  ;  and,  generally 
speaking,  the  temperatures  of  contiguous  spots  probably  tend  to 
equalize  each  other.  But  upon  the  whole,  the  influence  of  the 
lateral  propagation  of  heat  through  the  solid  parts  of  the  earth, 
must  be  very  limited. 

5.  Of  Ike  Propas^aflnn  of  Heat  and  Light  beloio  the  Earth'' s 
Surface  ui  Wafer.  VV-jter  is  a  very  imperfect  conductor  of  heat 
in  the  usual  acceptation  of  the  term.  Thus,  almost  any  degree  of 


PROPAGATION  OF  HEAT,  ETC,  BY  WATER.  147 

heat  may  be  applied,  for  a  considerable  time,  to  the  upper  surface 
of  a  mass  of  water,  without  materially  influencing  the  tempera- 
ture below  ;  so  imperfectly  and  slowly  is  heat  conducted  through 
this  fluid.  The  process  by  which  heat  is  communicated  through 
water,  we  have  termed  convection.  When  heat  is  applied  to  the 
bottom  of  a  vessel  full  of  this  fluid,  the  portion  of  the  water  first 
heated  expands  in  bulk,  and  thus  becomes  specifically  lighter  ;  it 
then  rises  to  the  top,  carrying  with  it  the  newly  acquired  tem- 
perature, while  another  cold  portion,  sinking  to  the  bottom,  is 
heated  in  turn,  and  so  on,  till  the  whole  mass  becomes  uniformly 
heated. 

With  respect  to  the  propagation  of  light  through  water,  it  has 
been  calculated  that  not  a  tenth  part  of  the  incident  light  can  ad- 
vance five  fathoms  dovv'nwards  in  the  most  translucent  water  ;  that 
even  of  vertical  rays,  one  half  is  lost  in  the  first  seventeen  feet, 
and  that  they  become  reduced  to  one-fourth  by  traversing  thirty- 
four  feet,  which  correspond  to  the  mass  of  an  atmosphere.  It 
thus  follows,  that  only  the  hundred  thousandth  part  of  the  verti- 
cal rays  can  penetrate  below  forty-seven  fathoms,  which  is 
scarce!}'  equal  to  the  glimmer  of  twilight  ;  and  that  the  depths  of 
the  ocean  must  be  always  in  perpetual  darkness.-^ 

Such  are  the  general  principles  by  which  heat  and  light  are 
propagated  in  water.  But  in  speaking  of  this  fluid  in  a  former 
chapter,  we  alluded  to  one  of  the  physical  properties  of  water,  of 
the  utmost  importance  in  the  economy  of  nature,  and  which, 
perhaps,  almost  more  than  anything  else,  indicates  design  ;  since, 
like  the  composition  of  the  atmosphere,  this  property  of  water 
constitutes  an  exception,  as  it  were,  to  a  general  law,  expressly 
directed  to  a  particular  object.  We  have  mentioned  that  it  is  a 
general  law,  that  all  bodies,  in  every  state  of  aggregation,  expand 
by  heat  and  contract  by  cold  ;  now  water  forms  a  marked  excep- 
tion to  this  law.  Like  other  bodies,  water  continues  to  contract 
on  the  removal  of  heat,  till  its  temperature  comes  down  to  within 
a  certain  distance  (7°  or  8°)  from  its  freezing  point.  At  this 
distance,  water  begins  again  to  expand,  and  the  expansion  con- 
tinues till  it  becomes  ice  ;  at  which  moment  of  freezing,  a  sudden 
and  considerable  expansion  takes  place.  Hence,  the  specific 
gravity  of  ice  is  decidedly  less  than  that  of  water,  and  the  solid 
necessarily  swims  on  the  surface  of  the  fluid.  The  importance 
of  this  anomalous  property  of  water  is  so  great,  that  it  is  doubt- 
ful whether  the  present  order  of  nature  could  have  existed  with- 
out it,  even  although  everything  else  in  the  world  had  remained 
the  same.  For  instance,  were  it  not  for  the  comparative  lightness 
of  ice,  this  solid,  instead  of  beginning  to  be  formed  at  the  surface 

*  Article  Climate,  in  the  Encyclopjedia  Britannica. 


148  METEOROLOGY. 

of  water,  would  have  begun  to  be  formed  at  the  bottom;  as  the 
colder  water  from  its  greater  specific  gravity  would  naturally 
have  sunk:  for  similar  reasons,  also,  the  lowest  stratum  of  ice 
would  have  been  the  last  to  have  melted.  Now,  let  us  reflect  for 
a  moment  upon  the  consequences  of  such  an  arrangement.  In 
the  northern  and  indeed  even  in  temperate  climates,  the  bottoms 
of  all  lakes  and  deep  waters  would  have  been  a  mass  of  ice,  and 
totally  inaccessible,  therefore,  to  organized  beings.  During  the 
summer  a  few  feet  of  the  upper  part  of  the  ice,  would,  perhaps, 
have  been  melted  ;  but  what  little  had  thus  become  melted  in 
summer,  would  again  have  become  solid  during  winter  ;  and  as 
the  accumulations  of  ice  would  have  been  constant,  all  the  seas, 
even  perhaps  to  the  tropical  climates,  at  least  at  their  bottom, 
would,  long  before  this  time,  have  been  a  mass  of  ice  !  But 
what  in  reality  happens  ?  In  consequence  of  the  above  anomalous 
properties  of  water,  this  mischief  is  entirely  prevented,  and  not  a 
particle  of  ice  can  be  formed  in  a  lake  or  other  collection  of  water, 
till  the  whole  mass  is  cooled  down  to  the  temperature  of  40°,  at 
which  temperature  the  specific  gravity  of  water  is  at  its  maxi- 
mum. 

These  properties  of  water  operate  in  the  following  manner. 
On  the  application  of  cold  to  the  surface  of  water,  the  cooled 
portion  sinks,  and  its  descent  forces  up  a  portion  of  warmer  water 
to  the  surface,  which  after  communicating  some  of  its  heat  to  the 
superincumbent  air,  sinks  in  its  turn ;  and  this  process  goes  on 
for  a  greater  or  less  time  according  to  the  depth  of  the  water.  If 
the  depth  be  not  very  considerable,  the  whole  body  of  water  be- 
comes cooled  down  to  40°;  at  which  temperature  the  specific 
gravity  not  increasing,  the  circulation  ceases,  and  the  surface  of 
the  water,  (not  the  bottoin)  becomes  at  length  so  far  cooled  as  to 
be  covered  with  ice.  If  the  depth  of  the  water  be  considerable, 
the  application  of  cold  may  be  long  continued  without  the  result 
of  freezing  ;  hence,  in  this  and  in  other  countries,  not  intensely 
cold,  it  often  happens  that  deep  lakes  remain  unfrozen  during  the 
coldest  winters. 

The  above  anomalous  properties  of  the  expansion  of  water  and 
its  consequences,  have  always  struck  us  as  presenting  the  most  re- 
markable instance  of  design  in  the  whole  order  of  nature — an  in- 
stance of  something  done  expressly  and  almost  (could  we  indeed 
conceive  such  a  thing  of  the  Deity),  at  second  thought,  to  accom- 
plish a  particular  object.  Further,  if  in  conjunction  with  this 
anomalous  property  of  water,  we  take  into  account  the  still  more 
anomalous  constitution  of  atmospheric  air,  and  at  the  same  time 
consider  the  relations  of  water  and  air  to  organic  existence,  we 
are  unavoidably  driven  to  the  conclusion,  that  the  Maker  of  water 
and  of  air  has  designedly  created  these  anomalies,  to  obviate  dif- 


PROPAGATION  OF  liEAT  BY  WATER.  149 

ficuliies  which  would  have  rendered  organic  existence  a  physical 
impossibility.  TJius,  had  means  not  been  taken  to  secure  the 
fluidity  of  water  under  the  varying  circumstances  of  temperature 
in  which  it  is  placed  ;  the  greater  portion  of  this  fluid  in  the  world 
would  long  ago  have  been  a  solid  mass  of  ice,  and  consequently 
inaccessible  to  organic  life.  Had  means  not  been  taken  to  secure 
the  homogeneity  of  air  at  all  times,  and  under  all  circumstances  ; 
this  important  medium  would  not  only  have  been  constantly 
liable  to  local  deteriorations  ;  but  its  properties,  long  ere  now, 
would  have  probably  become  deteriorated  to  such  a  degree,  as  to 
have  rendered  the  permanence  of  organic  life  not  less  physically 
impossible.  Nor  do  the  suppositions  which  the  sceptic  will  urge, 
that  these  properties  of  water  and  air  flow  naturally  from  their 
constitution,  diminish  the  force  of  the  argument.  The  force  of 
the  argument  lies,  in  the  first  place,  in  the  fact  that  water  and  air 
have  been  created  with  such  anomalous  properties  ;  and,  in  the 
next  and  chief  place,  that  these  anomalous  properties  have  been 
brought  into  action  precisely  where  they  are  required.  Moreover, 
the  argument  is  greatly  strengthened,  by  the  fact  that  two  ano- 
rnalies,  rather  than  that  two  ordinary  circumstances,  have  been 
thus  expressly  adjusted. 

Having  stated  the  general  principles  on  which  heat  is  distri- 
buted through  water,  and  its  most  remarkable  consequence ;  we  are 
now  to  enter  into  a  few  details  with  respect  to  some  other  conse- 
quences of  this  distribution.  Of  these  one  of  the  most  striking 
is,  that  the  temperature  of  the  water  at  the  bottoms  of  deep  lakes 
or  inland  seas,  must  remain  nearly  unilorm  during  the  whole  year. 
Thus  it  has  been  found  that  the  temperature  of  the  water  at  the 
bottoms  of  many  of  the  lakes  in  Switzerland  often  varies  no  more 
than  3°  or  4°,  while  the  temperature  of  the  surface  often  varies 
20°  or  30"^.  Hence  in  deep  waters,  in  temperate  climates,  the 
changes  of  temperature  are  chiefly  confined  to  the  upper  strata  of 
the  water ;  nor  can  ice  (except  from  some  very  sudden  and  pow' 
erful  accessions  of  frost)  form  on  the  surface  of  such  a  lake,  till, 
as  before  observed,  tlie  whole  of  the  water  in  it  is  cooled  down  to 
40°,  at  which  temperature  all  circulation  ceases.  When  a  coat 
of  ice  has  been  once  formed,  this  ice,  as  we  shall  see  presently, 
has  also  a  powerful  tendency  to  prevent  the  further  cooling  of 
the  inferior  strata. 

With  respect  to  ivaters  in  motion,  as  small  streams,  or  rivers 
of  no  great  depth  and  magnitude,  and  containing  fresh  waters  ; 
though  unfavourably  circumstanced  for  freezing,  they  do  never- 
theless congeal.  The  process  usually  commences  at  the  shores 
where  the  water  is  shallowest,  and  its  motion  is  least  rapid  ; 
from  whence  the  ice  gradually  advances  towards  the  centre  of  the 
stream.     When  the  whole  of  the  surface  has  once  become  fixed, 

13* 


150  METEOROLOGY. 

congelation  goes  on  actively,  particularly  by  night.  As  the 
thickness  of  the  ice  increases,  however,  the  quantity  added  daily, 
even  supposing  the  cold  to  remain  the  same,  gradually  diminishes, 
on  account  of  the  bad  conducting  power  of  the  ice.  Hence  in  a 
block  of  ice  taken  from  a  river  or  lake,  we  may  often  observe  the 
strata  corresponding  with  the  daily,  or  rather  nightly  additions, 
presenting  a  gradually  decreasing  series  from  several  inches  down 
to  a  few  lines  in  thickness. 

Of  the  Temperature  of  the  Waters  of  the  Ocean  at  great 
Depths. — Between  the  Tropics,  the  temperatnre  of  the  ocean  di- 
minishes with  the  depth  ;  in  the  Polar  seas,  on  the  contrary,  the 
temperature  augments  with  the  depth.  In  the  temperate  seas, 
comprised  between  30°  and  70°  of  latitude,  the  temperature  of 
tlie  water  gradually  decreases  as  the  latitude  increases,  until 
about  the  latitude  of  70°  ;  when  the  temperature  begins  to  rise  as 
before  mentioned.  Hence  about  the  latitude  of  70°  there  exists 
a  zone  or  band  at  which  the  mean  temperature  of  the  ocean  is 
very  nearly  constant  at  all  depths.  The  temperatures  of  particu- 
lar parts  of  the  ocean,  however,  have  been  observed  to  be  much 
influenced  by  the  depth  and  extent  of  the  water,  particularly  in 
hio-h  latitudes. 

We  have  already  mentioned  the  influence  of  the  saline  matters 
of  the  ocean  upon  the  freezing  point  of  sea-water^  and  we  have 
now  to  point  out  the  important  consequence  of  this  property  in 
the  economy  of  nature.  In  its  natural  slate  sea-water  freezes  at 
about  28°  or  29°,  but  when  it  has  been  concentrated  by  previous 
freezing  the  congealing  point  is  reduced  to  15°  or  16°  ;  while  water 
saturated  with  salt,  it  is  said,  does  not  freeze  at  a  temperature 
above  5°.  Besides  this  property  of  lowering  the  freezing  point 
of  sea-water,  the  saline  matters  also  increase  its  specific  gravity 
and  its  point  of  maximum  density.  Hence  from  these  circum- 
stances, and  from  their  immense  depth  and  extent,  the  waters  of 
the  ocean  resist  freezing  still  more  efl^ectually  tiian  even  running 
fresh  water,  and  are  indeed  rarely  frozen,  except  in  latitudes  where 
the  most  intense  cold  prevails. 

Of  the  under  Currents  of  the  Ocean  existing  between  the 
Equatorial  and  Polar  Regions. — That  the  diminished  tempera- 
ture of  the  waters  of  the  ocean,  at  great  depths  near  the  equator, 
could  not  have  been  acquired  in  the  torrid  zone,  is  evident ;  nor, 
on  the  other  hand,  could  the  comparatively  liigh  temperature  of 
the  waters,  at  the  bottom  of  the  Polar  seas,  have  been  acquired 
in  the  frigid  zone  ;  at  least  this  high  temperature  of  the  Polar  seas 
cannot  be  caused  from  without.  Hence  it  has  been  supposed  that 
there  is  a  constant  interchange  going  on  between  the  waters  of 
the  Equatorial,  and  those  of  the  Polar  regions  ;  though  there  are 
considerable  difliculties  at  present  as  to  the  means  by  which  this 


TEMPERATURE  BY  LAND  AND  WATER.  151 

interchange  is  effected.  These  difficulties  arise  principally  from 
some  uncertainty  with  respect  to  the  point  of  maximum  density 
of  sea-water,  which  does  not  appear  lobe  satisfactorily  established. 
Whether  in  the  profound  and  comparatively  quiescent  abyss  of 
the  ocean,  the  process  of  diffusion,  or  the  central  heat  of  the  earth 
formerly  alluded  to,  exert  any  influence,  we  have  no  means  of 
determining.  But  if  a  central  heat  really  do  exist,  its  effects  must 
be  considerable,  particularly  within  the  frigid  zone.  Whatever 
be  the  cause  of  this  approach  to  uniformity  of  temperature  through- 
out the  waters  of  the  ocean,  at  great  depths  all  over  the  globe,  its 
use  in  the  economy  of  nature,  in  lending  to  equalize  the  distri- 
bution of  temperature,  cannot  be  questioned  ;  since  it  constitutes 
one  of  those  beautiful  provisions  by  which  the  difficulties  of  the 
distribution  of  temperature,  necessarily  incidental  to  the  earth's 
figure  and  moiions,  are  obviated  ;  whilst  among  the  minor  circum- 
stances contributing  to  the  same  end,  may  be  mentioned  the  tides 
and  the  innumerable  superficial  currents  produced  by  winds  and 
by  other  causes  which  are  to  be  considered  elsewhere. 

W^e  have  alluded,  in  a  former  chapter,  to  the  difference  of  tern- 
perature  as  depending  upon  whether  the  surface  be  land  or  sea; 
and  perhaps  it  m:iy  not  be  amiss,  in  this  place,  to  make  a  few  re- 
marks upon  the  actual  general  amount  of  the  differences  of  tem- 
perature, as  produced  by  land  and  water. 

In  the  middle  of  oceans,  and  far  from  the  influence  of  land,  the 
diurnal  change  of  temperature  of  the  air  near  the  surface  of  the  sea 
is  much  less  than  upon  land.  Thus,  in  the  equatorial  regions  the 
greatest  difference  between  the  temperature  of  the  day  and  that 
of  the  night  at  sea  is  said  to  amount  to  3^  or  4°  only  ;  while  upon 
land  the  difference  often  amounts  to  9°  or  10°.  In  temperate  re- 
gions, and  particularly  in  latitudes  extending  from  25°  to  50°,  the 
difference  between  the  maximum  and  the  minimum  diurnal  range 
of  the  thermometer  at  sea  is  slill  very  trifling,  amounting  only  to 
4°  or  6°  ;  wliile  upon  the  continents,  as  for  example,  at  Paris,  the 
range  often  amounts  to  20°  or  30°.  To  these  circumstances  it  is 
owing  that  small  insular  situations,  partaking  of  the  character  of 
the  surrounding  ocean,  are  much  less  liable  to  great  diurnal  changes 
than  continents ;  and  hence,  in  general,  they  possess  more  equa- 
ble climates. 

Both  by  sea  and  land  the  minimum  temperature  takes  place 
about  sunrise.  The  maximum  temperature  at  sea  occurs  about 
noon,  or  very  soon  after  ;  while  upon  land  it  takes  place  from  two 
to  three  hours  after  noon.  Between  the  tropics  the  maximum 
temperature  of  the  air  is  said  to  exceed  a  little  that  of  the  surface 
of  the  sea.  But  when  the  temperatures  are  observed  at  short  in- 
tervals, as  for  example,  every  four  hours,  and  all  the  temperatures 
are  compared,  the  results  are  different;  and  ihey  seem  to  show 


152  METEOROLOGY. 

iliiit  even  between  the  tropics  tlie  temperature  of  the  surface  of  the 
sea  is  higher  than  that  of  the  incumbent  atmosphere.  Between 
the  latitudes  of  25°  and  50°  the  air  is  rarely  warmer  than  the  sur- 
face of  the  sea  ;  and  in  the  Polar  regions  it  is  very  unusual  to  find 
the  air  as  warm  as  the  sea  ;  it  is  in  fact  almost  always  colder,  and 
generally  very  much  colder. 


As  connected  with  this  part  of  our  subject,  it  may  perhaps,  be- 
fore we  close,  be  desirable  to  offer  a  few  remarks  upon  the  tem- 
perature of  natural  springs,  and  their  relation  to  the  mean  tem- 
perature of  the  earth  at  the  places  where  they  make  their  appear- 
ance. 

Springs  discharging  large  quantities  of  water,  and  thus  indicating 
that  ihey  come  from  considerable  depths  below  the  surface  of  the 
earth,   preserve  nearly  the  same  temperature  during  the   v/hole 
year.   In  our  hemisphere,  what  little  augmentation  of  temperature 
springs  undergo,  is  generally  in  the   month  of  September,   while 
they  are  coldest  in  the  month  of  March  ;    though  the  differences 
seldom  exceed  two  or  three  degrees.  If  w^e  compare  the  temperature 
of  the  springs  of  any  place,  with  the  mean  annual  temperature  of 
that  place,  we  find  that  there  is  a  near  connection  between  the  two, 
all  over  the  globe.    In  the  torrid  zone,  however,  the  mean  annual 
temperature  of  the  air  is  usually  higher  by  three  or  four  degrees 
than  that  of  the  springs  ;  v/hile  in  the  temperate  zone,  on  the  con- 
trary, the  springs  are  warmer  than  tlie  air.     The  excess  of  tem- 
perature of  springs,  as  compared  with   the  mean  annual  tempera- 
ture, goes  on  increasing  with  the  latitude  ;  so  that,  between  60° 
and  70°  of  latitude,   this  excess  amounts  to  from  5°  to  7° ;  a  cir- 
cumstance we  sliall  again  have  occasion  to  notice.     Other  things 
being  the  same,  the  temperature  of  springs  varies  considerably  ac- 
cortiing  to  ilieir  copiousness;  as  a  large  body  of  water  will  be  less 
liable  to  be  influenced  by  the  surrounding  soil,  than  a  smaller  body 
of  water;  and  may  even,  in  turn,  influence  the  temperature  of  the 
soil  itself. 

The  subject  of  thermal  springs,  as  intimately  connected  with 
the  history  of  volcanoes,  belongs  to  the  Geologist. 

We  have  thus  enumerated  the  principal  circumstances  connected 
with  the  distribution  of  temperature  upon  the  surface  of  the  earth, 
and  at  such  parts  below  it  as  are  within  our  reach.  We  now  come 
to  the  second  great  division  of  the  subject  of  climates  ;  viz.,  that 
connected  with  the  atmosphere. 


DISTRIBUTION  OF  HEAT  IN  THE  ATMOSPHERE.  153 


Section  II. 

Of  the  Secondary  Constituents  of  Climate  immediately  connected 

with  the  Atmosphere. 

The  phenomena  of  the  atmosphere  originally  constituted  the 
proper  study  of  the  Meteorologist,  and  even  yet  they  claim  the 
largest  share  of  his  attention,  'i'he  subject,  in  all  its  bearings, 
is  very  extensive,  and  many  of  the  details  are  imperfectly  under- 
stood. We  shall  endeavour  to  present  a  brief  outline  of  t!ie  prin- 
cipal phenomena  under  the  following  heads. —  Of  the  distribution 
of  heat  and  of  light  through  the  atmosphere,  and  of  the  conse- 
quences;— of  the  distribution  of  water  through  the  atmospherej 
and  of  the  phenomena  dependent  upon  this  distribution;  and, 
lastly, — of  the  occasional  presence  of  foreign  bodies  in  the  at- 
mosphere. 

1.  Of  the  Distribution  of  Heat  and  of  Light  through  the  At- 
mosphere, and  of  the  Consequences. — Every  one  is  familiar  with 
the  general  fact  of  the  diminished  temperature  of  the  higher 
regions  of  our  atmosphere  ;  and  that  in  the  hottest  countries,  by 
ascending  a  lofiy  mountain,  we  encounter,  at  diflerent  heights, 
every  variety  of  temperature,  even  to  that  of  perpetual  snow,  and 
of  the  Polar  regions.  One  of  the  first  circumstances,  therefore, 
that  claims  the  attention  of  the  Meteorologist,  is  the  law  of  tliQ 
distribution  of  sensible  heat,  or  of  temperature,  through  the  atmo- 
sphere. 

The  law  of  the  distribution  of  temperature  through  the  atmo- 
sphere is  tolerably  uniform,  though  it  is  occasionally  liable  to 
variations  and  interruptions,  depending  upon  local  difTerences, 
and  perhaps  upon  other  circumstances,  not  satisfactorily  under- 
stood. The  mean  results  of  a  great  number  of  observations  made 
in  different  parts  of  the  world  appear  to  show,  that  for  every  100 
yards  of  altitude,  Fahrenheit's  thermometer  sinks  one  degree. 
This  statement,  probably,  does  not,  within  moderate  limits,  differ 
much  from  the  truth  ;  though  some  late  researches  have  rendered 
it  probable  tliat  while  at  different  heights  the  rate  of  the  decrease 
of  temperature  is  uniform,  the  rate  of  altitude  increases  constantly, 
and  according  to  laws  very  similar  all  over  the  world  ;  that  is  to 
say,  supposing  the  first  252  feet  are  equal  to  one  degree,  the 
second  degree  will  be  equal  to  255  feet,  the  third  to  258,  the 
fourth  to  261,  &;c. 

The  causes  upon  which  tins  great  cold  of  the  higher  regions 
depends  are  chiefly  the  two  following;  first,  the  perfect  permea- 
bility of  the  atmosphere  to  the  solar  rays,  on  which  account  they 
radiate  through  it  almost  without  affecting  its  temperature,  till 


154  METEOROLOGY. 

reacliing  t!ie  earlli  they  exert  their  utmost  force  ;  and  secondly 
the  increased  capacity  for  heat  which  air  possesses  in  proportion 
as  it  becomes  more  ran^.  From  the  first  of  these  causes  it  hap- 
pens that  the  temperature  of  the  lower  regions  of  the  atmosphere 
is  derived,  not  immediately  from  the  sun,  but  from  the  earth.  The 
earth  absorbing  the  solar  heat,  recommunicates  it  to  that  portion 
of  the  atmosphere  immediately  incumbent  on  the  surface,  while 
all  the  atmosphere  above  remains  unaffected;  for  though,  from 
diminished  specific  gravitj^  heated  air  naturally  ascends,  yet  as 
its  capacity  for  heat  at  the  same  time  increases,  ascending  air 
rapidly  loses  its  sensible  heat :  as  in  the  second  place  we  have  to 
explain. 

Dr.  Dalton,  and  afterwards  Sir  Jolin  Leslie  more  completely, 
have  attempted  to  show  that  the  equilibrium  of  heat  in  the  atmo- 
sphere is  obtained  ivhen  each  of  its  molecules,  or  in  other  words, 
when  the  same  rveighl  of  air,  in  the  same  perpendicular  column, 
is  possessed  of  the  same  quantify  of  heat.  Now,  since  atmo- 
spheric pressure  diminishes  with  tiie  height  according  to  a  certain 
law,  it  is  obvious  that  the  same  iveigkts  of  air  at  the  surface  of 
the  earth,  and  in  the  higher  regions,  ^w'\\\  occupy  very  different 
spaces.  But  since  the  absolute  quantity  of  heat  is  exactly  the 
same  in  both  portions,  it  is  likewise  obvious  that  in  the  higher 
regions  of  the  atmosphere,  from  the  increased  capacity  of  the  air 
for  heat,  the  quantity  of  latent  heat  is  gradually  augmented,  while 
the  quantity  remaining  sensible,  becomes  less.  Hence  the  tem- 
peratuie  of  the  air  diminishes  as  we  ascend,  exactly  in  the  pro- 
portion that  its  latent  heat,  that  is  to  say,  its  capacity  for  heat  as 
produced  by  rarefaction,  increases.  In  consequence  of  this  ar- 
rangement, to  use  the  words  of  Dr.  Thomson,  "if  a  quantity  of 
cold  air  were  suddenly  transported  from  an  elevated  region  to  the 
surface  of  the  sea,  its  density  would  be  continually  increasing 
during  its  descent,  while  its  latent  heat  would  diminish  in  the 
same  proportion  ;  and  when  it  reached  the  level  of  the  sea  its  tem- 
perature would  be  just  as  high  as  that  of  other  portions  of  air  in 
the  same  latitude  and  elevation.  Air,  therefore,  does  not  feel  cold  in 
consequence  of  falling  from  an  elevated  situation,  though  this  be 
an  opinion  commonly  entertained,  but  in  consequenee  of  its  being 
suddenly  transported  from  a  more  northerly  to  a  more  southerly 
situation."^  Thus,  to  the  above  beautiful  and  simple  law,  we 
owe  the  permanent  state  of  equilibrium  of  temperature  in  the 
atmosphere  ;  for,  in  spite  of  all  the  disturbances  constantly  pro- 
duced by  minor  causes,  this  equilibrium,  from  the  natural  tendency 
to  right  itself,  is  never  very  seriously  afrected. 

Of  the  Limits  of  Perpetual  Snow. — Connected  with  the  dimi- 

*  On  heat  and  electricity,  p,  129. 


LIMITS  OF  PERPETUAL  SNOW  ;    GLACIERS.  155 

nution  of  temperature  in  the  liigher  regions  of  the  atmosphere  are 
the  limits  of  perpetual  snow  m  different  latitudes.  These  limits, 
of  course,  may  be  naturally  supposed  to  follow  the  mean  tempe- 
rature of  32°,  from  the  level  of  the  sea  in  the  Polar  regions  to 
the  highest  point  of  their  range  under  the  equator.  This  infer- 
ence is  obvious,  and,  genenilly  speaking,  correct  ;  though  it  is 
liable  to  certain  modifications,  and  to  some  anomalies,  of  which 
the  following  are  the  most  remarkable. 

Under  the  equator  the  limits  of  perpetual  snow  are  the  most 
fixed  and  steady,  and  seem  to  exist  generally  at  an  altitude  of  be- 
tween 15,000  aiid  16,000  feet.     As  we  recede  from  the  equator, 
the  oscillations  for  the   most  part  become  more  striking,  and  all 
the  phenomena  assume  a  more  irregular  form.    Such,  for  example, 
is  the  case  in  the  Mexican  Cordilleras  ;  but  still   more  evidently 
in  the  Himmala  range,  where  there  is  a  differeuce  of  no  less 
than  4000  feet  between  the  limits  of  perpetual  snow  on  the  north- 
ern and  on  the  southern  sides  of  the  mountain,  that  on  the  north- 
ern being  the  higliest.     As   we  proceed  towards   the  temperate 
zones,   we  find,  in  mountainous  countries,  below  the  limits  of 
perpetual  snow,  immense  bodies  of  ice,  or  glaciers^  as  they  are 
termed.     These  glaciers  are  formed  by  the  alternate  melting  and 
congealing  of  the  extensive  beds  of  snow  that  lie  above  them. 
The  glaciers,  accumulating  in  vall^s,  are  often  by  the  enormous 
and  increasing  weight  of  the  snow  and  ice  in  the  upper  parts, 
pressed    downwards    far    beyond    the    limits  of   the  snow  itself. 
Such  are  the  glaciers  of  Switzerland,  of  Norway,  and  of  other 
countries  in  temperate  climates.     All  these  circumstances,  with 
others  that  might  be  mentioned,  and  many  probably  that  are  un- 
known to  us,  combine  to  render  the  limits  of  perpetual  snow  ir- 
regular.    These  irreffularities  are  so   great,  that  Humboldt  has 
given  as  a  mean  of  many  observations,   that  at  the  equator  the 
limits  of  perpetual  snow  are  nearly  3°   above  the  freezing  point, 
while  in  the  temperate  zone  they  are  nearly  5°  below  that  point, 
and  in  the  frigid  zone  no  less  than   10°  or  11°   below  freezing  ; 
which  observations  seem  to  pro\^e  that  the  general  temperature  of 
the  air  decreases  in  the  equatorial,  otherwise  than  in  the  colder 
regions.   From  the  peculiar  distribution  of  the  land  in  the  southern 
hemisphere,  little  is  known  of  the  Ihie  of  perpetual  snow  in  that 
part  of  the   world  ;  but  it  will  probably  be  found  to  be  different 
from  that  in  the  north,  and  generally  lower. 

The  perpetual  snow  resting  on  the  tops  of  mountains  consti- 
tutes a  most  important  provision  in  the  economy  of  nature,  par- 
ticularly in  the  warmer  climates,  where  the  accumulated  snow 
becomes  the  prolific  source  of  innumerable  rivers  without  which 
those  regions  wonld  be  uninhabitable. 

There  is  a  striking  difference  between  the  elevated  and  the 


156  METEOROLOGY. 

lower  regions,  which  must  have  considerable  influence  upon  or- 
ganization, though  this  influence  has  not  been  studied  so  carefully 
as  it  ought  to  be  ;  viz.,  the  difference  of  atmospheric  pressure. 
At  the  surface  of  the  earth,  the  atmospheric  pressure  is  nearly  the 
same  in  all  latitudes,  but  as  we  ascend  above  the  surface,  the 
pressure  rapidly  diminishes.  Everything  else,  therefore,  being 
supposed  to  be  the  same,  the  difference  of  pressure  is  probably 
alone  sutficient  material!)'  to  influence  organization,  and  to  render 
certain  provisions  and  accommodations  necessary,  of  which,  at 
present,  we  are  ignorant ;  but  which  might  be  doubtless  much  elu- 
cidated by  a  careful  study  of  Alpine  plants  and  animals,  as  com- 
pared with  those  that  occupy  the  plains. 

Of  the  Distribution  of  Heat  and  Light  through  the  Atmo- 
sphere in  their  latent  and  decomposed  Forms. — In  the  preceding 
paragraphs  we  have  alluded  to  the  quantity  of  heat  existing /a/e?7^  in 
the  higher  regions  of  the  atmosphere.  But  besides  this  quantity, 
which  may  be  supposed  to  be  common  to  the  whole  atmosphere, 
the  distribution  of  latent  heat  and  light  must  in  some  degree  follow 
the  same  law  as  that  of  sensible  heat  and  light ;  that  is,  must  de- 
crease from  the  equator  toward  the  poles.  Thus  there  can  be  no 
doubt,  that  the  expanded  air  of  the  equatorial  regions  contains 
much  more  heat  and  light  in  the  latent  state,  than  the  comparatively 
dense  and  dry  atmospheric  air  of  the  Polar  regions  ;  and  it  is  pro- 
bable that  the  rigours  of  each  extreme  are  mitigated  by  this  pro- 
vision. The  distribution  of  electricity  through  the  atmosphere 
seems  also  to  be  regulated  by  very  similar  laws.  It  may,  how- 
ever, be  remarked  that  the  effects  of  heat  and  light,  in  the  latent 
and  decomposed  forms,  are  much  more  striking  as  connected  with 
the  water  in  the  atmosphere,  than  with  the  constituents  of  the  at- 
mosphere itself.  We  shall,  therefore,  defer  what  we  have  to  say 
on  those  subjects  till  we  speak  of  the  water  in  the  atmosphere. 

Of  the  Propagation  of  Sensible  Heat  through  the  Atmo- 
sphere.— x\s  the  difl^usion  of  gaseous  bodies  through  each  other  is 
so  far  a  mechanical  process  that  it  is  regulated  solely  by  the  rela- 
tions of  their  specific  gravities,  it  follows  that  under  the  same  pres- 
sure, different  portions  of  the  same  gas,  having  different  tempera- 
tures, and  consequently  different  specific  gravities,  will  have  a 
similar  tendency  to  dilfusion.  Hence,  independently  of  all  other 
circumstances,  the  warm  and  light  air  of  the  equatorial  regions 
has  a  natural  tendency  to  diff'use  itself  toward  the  poles  ;  while 
the  colder  and  heavier  air  of  the  poles  possesses  a  similar  tendency 
to  dilfuse  itself  towards  the  equator,  though  in  a  greatly  mitigated 
degree.  The  exact  amount  of  these  tendencies  we  have  no  means 
of  estimating,  but  they,  doubtless,  exert  considerable  influence  ; 
and,  as  the  diffusive  power  may  happen  to  coincide  with,  or  op- 
pose the  atmospheric  currents,  to  be  next  considered,  it  may  aug- 
ment or  diminish  their  effects. 


PROPAGATION  OF  HEAT  IN  THE  ATMOSPHERE.  157 

Though  difTusion  be  thus  largely  concerned  in  the  lateral  pro- 
pagation of  temperature  through  the  atmosphere,  this  propagation 
is  evidently  affected  to  a  much  greater  extent  by  the  {)rocess  termed 
convection.  Convection,  like  diffusion,  of  course,  implies  motion 
or  currents  ;  which  currents  as  existing  in  the  atmosphere,  we 
need  scarcely  observe,  are  denominated  Winch.  The  winds, 
therefore,  are  of  the  utmost  importance  in  the  economy  of  nature, 
as  tending  to  equalize  the  distribution  of  temperature  over  the 
globe  ;  and  the  fohowing  brief  explanation  will  serve  to  give  a  ge- 
neral knowledge  of  their  nature. 

Atmospheric  currents  may  be  considered  under  two  heads  :  those 
of  a  general  kind,  and  which  extend  more  or  less  over  the  whole 
globe  ;  and  those  depending  upon  various  transient  derangements 
of  the  distribution  of  temperature,  tlie  effects  of  which  are  limited 
to  particular  localities.  On  each  of  these  we  shall  make  a  few  re- 
marks. 

The  general  currents  of  the  atmosphere  depend  principally  up- 
on the  two  following  circumstances,  which,  if  borne  in  mind  by 
the  reader,  will  furnisli  him  with  a  clue  to  tlie  whole  subject : 
viz.,  the  unequal  temperature  of  the  equator  and  of  the  poles  ;  and 
the  diurnal  motion  of  the  earth  upon  its  axis.  The  conveclive 
operation  of  the  first  of  these  general  causes  may  be  thus  illustrated. 
We  have  stated  that  the  entire  pressure  of  the  atmosphere  all  over 
the  earth's  surface  is  nearly  the  same,  and  equal  to  that  of  a 
column  of  mercury  about  thirty  inches  in  height.  We  have  also 
stated  that  the  mean  temperature  of  this  atmosphere  near  the  equa- 
tor, and  at  the  level  of  the  sea  is  upwards  of  80°,  whde  in  the  Po- 
lar regions  it  is  constantly  below  32°,  the  freezing  point  of  water. 
Hence,  as  air  expands  by  lieat,  and  becomes  specifically  lighter, 
it  is  obvious  that  a  given  bulk  of  air  at  the  level  of  the  sea  round 
the  poles,  must  be  considerably  heavier  than  a  similar  bulk  of  air 
at  the  level  of  the  sea  under  the  equator.  The  air,  therefore,  round 
the  poles  being  colder  and  heavier,  will  have  a  tendency  to  flow 
along  the  earth's  surface  from  the  poles  towards  the  equator,  and 
to  displace  the  lighter  air  under  the  equator;  whiie  the  equatorial 
air  so  displaced,  will,  owing  to  its  lightness,  ascend  and  flow  back 
a2[ain  over  llie  colder  air,  north  and  south  toward  the  poles,  so  as 
to  preserve  the  equilibrium.  Moreover  these  currents  will  be  per- 
petual ;  for  the  heat  of  the  equator  and  the  cold  of  the  poles  being 
constant,  the  same  tendency  to  change  will  always  exist,  and  thus 
the  currents  will  be  constant  likewise. 

These  atmospheric  currents  constitute  one  primary  element  of 
the  winds,  and  are  the  grand  means  by  which  the  equalization  of 
temperature  over  the  globe  is  effected.  If  the  earth  were  at  rest, 
and  its  surface  free  from  irregularity,  these  currents  or  winds  would, 
of  course,  be  in  the  northern  hemisphere  always  due  north,  and 

14 


158  METEOROLOGY. 

in  the  southern  hemisphere  clue  south  ;  while  the  velocity  would 
in  each  case  gradually  diminish  from  the  poles  towards  the  equa- 
tor, where  there  would  be  a  perpetual  calm. 

But  the  earth  is  in  a  constant  state  of  motion  upon  its  axis  from 
west  to  east,  by  which  motion  the  currents  are  deflected  from  their 
northern  and  southern  course  towards  the  east;  and  this  eastern 
deflection  constitutes  the  other  primary  clement  of  the  winds  to 
be  next  considered. 

On  the  surface  of  a  globe  revolving  like  the  earth  on  its  axis, 
the  general  reader  will  bear  in  mind  that  the  motion  of  any  given 
point  at  the  equator  is  t!ie  greatest^  and  at  the  poles  the  least  pos- 
sible. Thus  while  the  poles  are  quiescent,  the  velocity  of  any 
given  place  at  the  equator  of  our  earth,  is  about  1000  miles  an 
hour  ;  from  which  extreme,  the  velocity  gradually  diminishes  to- 
ward the  poles.  Tiiis  motion  of  the  earth  on  its  axis  operates  in 
the  production  of  an  easterly  current  in  the  atmosphere  as  follows. 
Supposing  there  were  no  atmospheric  currents  from  the  north  and 
south  towards  the  equator,  and  that  the  earth  revolved  upon  its 
axis  as  at  present,  one  of  two  things  must  happen.  Either  the 
earth  during  its  revolution  would  carry  with  it  the  incumbent  at- 
mosphere ;  in  which  case  there  would  be  a  perpetual  calm  over 
its  surface  :  or  the  earth  would  revolve  within  the  atmosphere, 
leaving,  as  it  were,  the  atmosphere  behinii  it :  in  which  case  there 
would  be  an  apparent  current  or  wind  over  the  whole  of  the  earth's 
surface,  in  a  direction  opposite  to  that  of  the  earth's  motion,  that 
is  from  east  to  west;  which  wind,  supposing  the  atmosphere  did 
not  move  with  the  earth,  would,  of  course,  be  at  its  maximum  at 
the  equator.  Now  both  these  causes  are  continually  operating, 
and  give  origin  to  all  the  variety  of  the  eastern  currents  upon  the 
earth's  surface,  which,  with  the  northern  and  southern  currents, 
before  described,  conspire  to  produce  the  well  known  currents 
called  the  trade  winds.  Before  we  attempt  to  explain  the  trade 
winds,  their  phenomena  may  be  thus  briefly  described. 

The  trade  winds  in  the  AUantic  ocean  extend  to  about  28°  on 
each  side  of  the  equator.  At  their  extreme  northern  and  southern 
boundaries  these  winds  generally  blow  from  the  east ;  but  as  they 
proceed  towards  the  equator  from  the  north  and  from  the  south, 
they  gradually  pass  from  the  east  through  all  the  intermediate 
points  of  the  compass,  till  near  the  equator  they  become  in  the 
northern  hemisphere,  due  north,  and  in  the  southern  hemisphere 
due  south.  The  trade  winds  are  subject  to  some  slight  variations 
chiefly  arising  from  the  position  of  the  earth  with  respect  to  the 
sun.  On  these  variations  we  do  not  think  it  necessary  to  enlarge. 
The  general  phenomena  are  as  we  have  stated  them,  and  they, 
upon  the  principles  advanced,  appear  to  admit  of  the  following 
explanation : 


CURRENTS  IN  THE  ATMOSPHERE.  159 

In  the  temperate  regions  of  the  earth  tlie  winds  seem  to  obey 
no  certain  laws  ;  at  least  laws  so  determinate  as  those  of  the 
trade  winds.  But  about  the  tropics,  both  in  tlie  northern  and  in 
the  southern  hemispheres,  the  operation  of  the  double  currents 
and  motions  before  described,  becomes  distinctly  perceptible. 
Thus  about  the  tropics,  the  surface  of  the  earth  begins  to  move 
faster  than  the  incumbent  atmosphere  ;  and  hence  in  these  regions, 
the  prevailing  currents  are  from  the  east.  Indeed  near  the  tro- 
pics the  currents  are  nearly  due  east,  principally  on  account  of 
the  great  and  sotnewhat  sudden  change  of  temperature  produced 
by  the  vertical  sun  of  the  tropical  regions  ;  which  may  be  sup- 
posed to  interfere  \v\[h,  and  perhaps  to  check  momentarily,  the 
regular  progress  of  the  great  northern  and  southern  currents.  As  we 
proceed,  however,  towards  the  equator,  in  both  hemispheres,  the 
atmosphere  gradually  acquires  the  velocity  of  the  earth,  while  the 
intensity  of  the  eastern  current  diminishes  in  the  same  proportion, 
and  at  length  entirely  disappears.  At  the  same  time  the  currents 
from  the  north  and  the  south  continuing,  slowly  deflect  the  cur- 
rents, from  the  east  towards  the  north  in  the  northern  hemisphere, 
and  from  the  east  towards  the  south  in  the  southern  hemisphere, 
till  left  alone  by  themselves  the  polar  currents  proceed  onward  to 
the  equator,  as  if  the  motion  of  the  eaith  had  no  existence. 

The  first  clear  and  satisfactory  theory  of  the  great  atmospheric 
currents  or  winds  w^as  given,  we  believe,  by  Mr.  Daniell.  The 
tlieory  of  the  winds  was  subsequently  illustrated  by  Captain  Basil 
Hall,  in  his  interesting  essay  on  the  trade  winds,  to  which  for 
details  we  must  refer  the  reader.*  Before  we  quit  this  subject 
we  may  remark  that  Mr.  Daniell  traces  to  these  great  currents 
the  fluctuations  of  the  barometer,  and  all  the  innumerable  modifi- 
cations peculiar  to  different  localities  of  sea  and  land,  of  mountain 
and  plain.  For,  as  he  justly  observes,  in  the  nicely  balanced  state  of 
the  forces  producing  these  currents,  slight  irregularities  of  tempera- 
ture are  capable  of  causing  great  disturbances;  and  expansions  and 
contractions  acting  unequally  upon  the  antagonist  currents,  ope- 
rate by  deranging  the  adjustment  of  their  several  velocities.  Hence 
accumulations  in  some  parts,  and  corresponding  deficiencies  in 
others,  necessarily  arise  ;  and  occasion  fluctuations  in  the  baro- 
meter, far  surpassing  what  would  be  occasioned  by  the  whole 
vapour,  supposing  it  were  at  once  added  or  annihilated.  At  the 
same  time  these  irregular  distributions,  in  seeking  to  regain  the 
proper  level,  and  in  struggling  to  restore  the  equilibrium,  produce 
temporary  and  variable  winds,  which  modify  the  regular  currents 
and  often  reverse    their  courses,    particularly    in  the  temperate 

•  See  Meteorolog''ical  Essays  and  Observations,  by  J.  F.  Daniell,  Esq., 
Professor  of  Chemistry  in  King-'s  College,  &c.,  page  465,  second  edition; 


160  METEOROLOGY. 

regions;  where,  as  formerly  mentioned,  the  alternations  of  tempe- 
rature, and  the  fluctuations  of  the  barometer,  are  the  most  re- 
markable. 

Such  are  the  elements  of  the  general  currents  pervading  our 
atmosphere,  and  such  the  modes  in  M'hich  these  currents  obviate 
extreme  temperatures  and  their  consequences.  The  same  causes 
are  constantly  operating  in  different  forms  and  degrees,  so  as  to 
produce  all  the  infinite  variety  among  the  winds,  which  we  ob- 
serve in  nature.  These  are  so  numerous  and  diversified,  as  actu- 
ally to  bafiie  all  attempts  at  explanation  or  arrangement;  we  shall 
therefore  content  ourselves  with  one  instance  only,  by  way  of 
illustration,  viz.,  the  sea  and  land  breezes. 

The  explanation  of  what  are  denominated  the  sea  and  land 
breezes  is  very  obvious,  and  is  not  less  applicable  to  many  similar 
phenomena.  During  the  day,  the  surface  of  the  land  acquiring 
heat,  imparts  its  temperature  to  the  incumbent  air.  This  air  ex- 
panding in  bulk  becomes  specifically  lighter,  and  rises  in  conse- 
quence ;  while  the  cooler  air  from  the  surrounding  sea  rushes  in 
to  supply  its  place,  and  thus  produces  the  current  called  the  sea 
breeze.  During  the  night,  on  the  contrarj'-,  the  waters  of  the 
ocean  part  with  their  heat  much  more  slowly  than  the  land,  and 
the  reverse  action,  or  the  land,  breeze  takes  place.  In  hot  cli- 
mates near  the  sea-shore,  and  in  insular  situations,  these  alterna- 
tions constitute  a  most  agreeable  variet3^ 

2.  Of  the  Presence  of  JVater  in  the  Atmosphere. — In  tlie  fore- 
going section  we  have  endeavoured  to  give  an  outline  of  the  beau- 
tiful provisions  that  have  been  adopted  to  prevent,  by  means  of 
the  air  of  the  atmosphere,  the  consequences  necessarily  arising 
from  the  unequal  distribution  of  heat  and  light  over  the  globe. 
We  now  come  to  another  subject  of  not  less  importance,  viz., 
the  phenomena  depending  upon  the  existence  of  water  in  the 
atmosphere,  and  which,  taken  together,  principally  constitute  what 
we  emphatically  denominate  the  TV^eatlier. 

Of  the  Relations  of  the  fVafer  in  the  Atmosphere  to  Tempera- 
ture.— We  have  before  stated  the  fact,  that  water  has  a  tendency 
to  assume  the  elastic  form  at  all  temperatures.  From  the  tendency 
of  water,  thus  to  rise  "  above  the  Firmament,"  not  only  the  ocean, 
but  ice  and  snow,  are  unceasingly  contributing  their  supply  of 
moisture  to  the  air  ;  and  this  important  fluid,  so  indispensable  to 
vegetable  and  animal  existence,  is  distributed  over  the  surface  of 
the  whole  earth.  In  considering,  therefore  the  relations  of  the 
water  of  the  atmosphere  to  temperature,  the  phenomena  which 
first  claim  our  attention,  are  the  processes  by  which  water  is  taken 
up  and  again  separated  from  the  atmosphere  ;  that  is  to  say,  the 
processes  of  Evaporation  and  Condensation. 

In  treating  of  the  nature  of  Evaporation.,  the  questions  to  be 


EVAPORATION  AND  CONDENSATION.  161 

answered  at  the  outset  are, — Why  is  moisture  present  in  the  at- 
mosphere ?  By  what  force  is  its  presence  determined,  and  its 
quantity  limited  ?  The  reply  to  these  questions  depends  upon 
the  properties  of  matter  in  general,  and  of  vapour  in  particular,  as 
formerly  described  ;  which,  if  the  reader  bears  in  mind,  will  en- 
able him  readily  to  understand  what  follows. 

When  water  is  exposed  to  the  air  in  an  open  vessel,  the  mole- 
cules of  its  uppermost  or  superficial  stratum,  being  released  from 
the  influence  of  those  below  them,  have  a  natural  tendency  to  as- 
sume that  degree  of  polarity  which  is  appropriate  to  their  tempe- 
rature. Hence,  after  acquiring  the  latent  heat  necessary  to  pro- 
duce this  polarity,  either  at  the  expense  of  a  portion  of  their  own 
sensible  heat,  or  that  of  the  atmosphere,  the  superficial  molecules 
of  water  become  self-repulsive,  and  fly  off"  into  space  in  the  form 
of  vapour.  If  the  space  over  the  v/ater  be  circumscribed  and  be 
a  vacuum,  the  molecules  fly  off*  with  such  rapidity  as  instantane- 
ously to  fill  it.  But,  if  the  space  be  occupied  by  air,  or  be  of  in- 
definite magnitude,  the  molecules  fly  oft'  more  slowly,  so  as  gra- 
dually to  difTuse  themselves  through  the  whole  space  ;  quite  on 
the  same  principle,  and  in  the  same  manner,  that  one  gaseous 
body  is  diff'used  through  another. 

Such,  in  few  words,  may  be  deemed  a  simple  statement  of 
what  evaporation  is.  We  shall  next  proceed  to  inquire  into  the 
nature  and  operation  of  the  means  by  which  evaporation  not  only 
takes  place,  but  is  limited  within  certain  boundaries. 

In  a  former  chapter,  we  remarked,  thnt  the  elastic  force  exerted 
by  all  bodies  in  the  gaseous  state  bears  a  certain  relation  to  their 
temperature,  but  that  the  degree  of  this  elastic  force  varies  accord- 
ing  to  other  circumstances  ;  particularly  according  to  whether  the 
gaseous  body,  at  the  given  temperature,  be  capable  of  existing  in 
the  fluid  or  in  the  solid  states,  as  well  as  in  the  gaseous  state. 
Thus,  atmospheric  air,  at  the  temperature  of  32°  (and  indeed  at 
all  known  temperatures),  is  a  gaseous  body,  and,  under  ordinary 
circumstances,  exerts  an  ehistic  force  equal  to  the  weight  of  a  col- 
umn of  mercury  30  inches  high  ;  whereas,  at  the  same  temperature 
of  32°,  water  is  a  solid,  and  the  force  of  the  elasticity  of  its  va- 
pour  is  not  more  than  equal  to  about  l-5ih  of  an  inch  of  mercurv. 
But  at,  and  above  212°,  its  boiling  point,  water,  under  ordinary 
circumstances,  can  exist  only  as  a  gas  ;  and  in  this  gaseous  form, 
and  at  the  temperature  of  212°,  water  obeys  precisely  the  same 
laws,  and  exerts  the  same  elastic  force  as  atmospheric  air  would 
do  under  similar  circumstances.  Hence  it  will  be  readily  under- 
stood, that  the  law  of  the  elastic  force  of  vapour  below  212°,  is 
very  different  from  the  law  of  that  force  above  212°  ;  as  by  ex^ 
periment  is  found  to  be  the  fact. 

From  the  preceding  remarks  it  will  appear  that,  all  other  things 

14* 


162  METEOROLOGY. 

being  the  same,  the  tendency  of  water  to  assume  the  form  of  va- 
pour, or  the  rate  of  its  evaporation,  as  well  as  the  actual  quantity 
of  water  in  the  state  of  vapour  in  the  atmosphere,  will  increase  as 
the  temperature  increases.  The  exact  law  of  this  increase,  in  all 
its  details,  we  need  not  state.  It  is  suflicient  for  our  purpose  to 
observe,  that  at  all  temperatures  below  the  boiling  point  of  water, 
that  is  to  say,  at  all  common  atmospheric  temperatures,  while  the 
late  of  the  increase  of  temperature  is  slow  and  uniform,  or  in  an 
arithmetical  progression,  the  corresponding  rate  of  the  elastic  force 
of  vapour,  by  which  the  quantity  of  water  as  vapour  is  determined, 
increases  much  more  rapidly,  or  nearly  in  a  geometrical  progres- 
sion. This  important  fact  is  connected  with  several  most  inte- 
resting circumstances. 

The  phenomena  of  the  Condensation  of  vapour  from  the  at- 
mosphere, are  next  to  be  explained.  As  the  quantity  of  water  in 
solution  in  the  atmosphere  can  never  be  greater,  though  it  may 
be  less,  than  the  quantity  proper  to  the  temperature  ;  Avhen  vapour 
(or  what  is  the  same  thing,  when  a  portion  of  air  saturated  with 
vapour),  at  any  given  temperature,  is  cooled  below  the  point  of 
saturation  ;  a  portion  of  the  vapour  is  separated  in  the  form  of  fluid 
water,  while  the  remainder  assumes  the  elastic  condition  proper 
to  the  newly  acquired  and  diminished  temperature.  The  forms 
assumed  by  the  water  so  separated  are  various,  and  depend  very 
much  upon  the  quantity  separated,  and  on  the  separation  taking 
place  in  atmospheric  air.  When  the  quantity  of  water  separated 
is  small,  the  minute  detached  particles  diffused  through  a  large 
space,  are  suspended  in  ib.e  attnosphere  by  its  buoyancy,  and  as- 
sume the  form  of  what,  for  the  sake  of  distinction,  we  shall  call 
Visible  Vapour,  viz.  mists,  clouds,  &;c.  When  the  quantity  se- 
parated is  greater,  the  particles  collect  into  drops  too  large  to  be 
upheld  by  atmospheric  buoyancy,  and  they  fall  to  the  earth  in  the 
shape  of  rain,  hail,  &;c. 

Of  the  two  great  processes  of  evaj)oration  and  condensation,  it 
may  be  further  remarked,  that  by  a  beautiful  provision,  they  have 
a  constant  tendency  to  limit  each  its  own  operations  ;  evaporation 
is  increased  by  heat  and  produces  cold  ;  condensation  is  produced 
by  cold  and  liberates  heat.  Moreover,  in  virtue  of  another  won- 
derful arrangement,  by  evaporation,  water  is  separated  entirely 
from  all  forei'ni  bodies,  and  is  thus  condensed  in  a  state  of  abso- 
lute  purity. 

We  now  come  more  particularly  to  consider  the  subject  of  the 
vapour  of  the  atmo8})iiore.  To  facilitate  the  understanding  of  this, 
we  ^hall,  m  the  first  place,  suppose  the  air  to  be  absent,  and  shall 
inquire  what  would  be  the  covA\'nions  of  an  atmosphere  of  vapour, 
under  the  pressure  and  temperature  existing  at  the  surface  of  the 
earth,  and  at  different  heights  above  the  eartli's  surface. 

As  the  clastic  force  of  vapour  increases  faster  than  the  tempe- 


ATMOSPHERE  OY  VAPOUR.  163 

ratiire  of  the  vapour  ;  and  as  tlie  mean  temperalure  at  the  Equator 
is,  at  least,  80"",  and  that  at  the  Poles  below  32°  ;  it  follows,  that 
in  an  atmosphere  of  vapour,  heated  similarly  to  that  of  our  earth, 
the  specific  gravity  of  the  vapour  at  the  Equator,  would  greatly 
exceed  the  specific  gravity  of  the  vapour  at  the  Poles.  Vapour 
thus  exhibits  a  condition  directly  opposite  to  that  of  air,  under  the 
same  circumstances.  Hence  the  tendencies  of  the  currents,  and  of 
diffusion,  in  an  atmosphere  of  vapour,  at  the  surface  of  the  earth, 
would  be  precisely  the  reverse  of  those  in  an  atmosphere  of  air  ; 
the  tendency  of  the  currents  would  be  from  the  Equator  toward 
the  Poles,  while  the  tendency  of  diffusion  would  be  from  the  Poles 
toward  the  Equator.* 

We  have  elsewhere  stated  the  law  of  the  decrease  of  the  tem- 
peralure of  the  atmosphere,  observed  in  ascending  from  tlie  surface 
of  the  earth  ;  the  atmospheric  air  being  supposed  to  be  free  from 
moisture.  A  similar  law  would  regulate  the  decrease  of  tempera- 
ture in  an  atmosphere  of  vapour;  but  the  rate  of  decrease  would 
be  much  more  slow  than  in  an  atmosphere  of  perfectly  dry  air. 
Thus  under  the  Equator,  where,  at  tlie  level  of  the  sea,  the  mean 
temperature  is  at  least  80,  the  temperature  of  an  atmosphere  of 
perfectly  dry  air  would  sink  to  the  freezing  point  at  a  height  of 
15,000  feet;  while  tlie  temperature  of  an  atmosphere  of  vapour 
would,  at  the  same  height,  sink  only  to  70°.  At  all  the  parallels 
of  lower  mean  temperalure,  onv/ard  to  the  lowest  round  the  Poles, 
at  any  height  above  the  level  of  the  sea,  similar  differences  would 
exist  between  the  temperature  of  an  atmosphere  of  perfectly  dry 
air  and  the  temperature  of  an  atmosphere  of  vapour;  these  differ- 
ences, of  course,  varying  with  the  mean  surface  temperature.  At 
the  same  time,  throughout  the  whole  range,  from  the  Equator  to 
the  Poles,  the  specific  gravity  of  the  vapour  at  the  level  of  the  sea 
would  always  exceed  its  specific  gravity  at  any  height  above. 
Hence,  in  an  atmosphere  of  vapour,  there  would  be  no  vertical 
currents;  but  there  would  be  a  strong  tendency  to  diffusion  from 
above  downwards  ;  while  the  tendency  to  lateral  diffusion,  would, 
at  all  heights,  be  nearly  tlie  same  as  at  the  surface,  or  would  be 
quite  contrary  to  what  would  hold  in  an  atmosphere  of  perfectly 
drv  air. 

*  We  may  here  observe,  once  for  all,  that  our  former  remarks  on  the 
diffusion  of  air  of  different  temperatures,  and  om-  remarks  now  on  the  si- 
milar diffusion  of  \apour,  are  inferences  only  from  the  g'er.erai  law  of  dif- 
fusion ;  and  that  the  diffusion  of  such  fluids  has  not,  at  least  in  so  far  as  we 
know,  been  yet  the  subject  of  experiment.  We  do  not,  tlierefore,  think 
it  necessary  to  dwell  on  the  precise  law  of  this  diffusion.  Our  remarks 
have  been  chiefly  made  witii  tiie  view  of  drawing  the  attention  of  philo- 
sopiicrs  toward  these  interesting- phenomena.  Tl.e  diffusion  of  gases  and 
of  vapour,  taken  in  conjunction  with  the  diffusion  or  radiation  of  impon- 
derable matters,  would  form  a  noble  field  to  those  competent  for  such 
physical  inquiry. 


164  METEOROLOGY. 

Having  thus  stated  the  leading  properties  of  an  atmosphere  of 
air  and  of  an  atmosphere  of  vapour  separately,  we  come  to  the 
proper  subject  of  our  inquiry ;  viz.,  //^e  condition  of  an  atmosphere 
resulting  from  a  mixture  of  air  and  vapour — of  such  an  atmo- 
sphere, indeed,  as  that  in  which  we  actually  live. 

The  reader  will  have  no  difficulty  in  understanding  the  nature 
of  a  mixed  atmosphere,  provided  he  has  clearly  apprehended  what 
has  been  above  stated,  regarding  the  simple  atmospheres  which 
are  its  components,  and  will  advert  to  two  other  circumstances 
that  are  now  to  be  noticed.  These  two  circumstances  are  inti- 
mately connected  with  the  principles  previously  stated,  and  with 
each  other  ;  and  an  exposition  of  them  is  absolutely  necessary  for 
obtaining  a  true  knowledge  of  the  relations  of  an  atmosphere  of 
vapour  with  an  atmosphere  of  air.  These  circumstances  have 
not  been  mentioned  sooner,  the  consideration  of  them  having  been 
intentionally  delayed,  in  order  that  their  influence  might  be  seen, 
where  their  application  is  more  immediately  requisite.  They  are 
as  follow. 

When  vapour  and  air  are  mixed  together,  the  resulting  volume 
of  the  mixture  depends  on  the  amount  of  the  elastic  forces  of  the 
vapour  and  of  the  air ;  not  on  any  relation  between  their  volumes. 
Thus  when  a  cubic  foot  of  air  at  the  temperature  of  32^,  and  ex- 
erting an  elastic  force  equal  to  30  inches  of  mercury,  is  mixed 
with  a  cubic  foot  of  vapour,  having  the  same  temperature,  and  ex- 
erting an  elastic  force  equal  to  only  l-5th  of  an  inch  of  mercury; 
the  volume  of  the  mixture  resulting  is  not  two  cubic  feet,  but  only 
1-0066  foot.  Hence,  as  the  addition  of  vapour  to  air  adds  com- 
paratively little  to  the  bulk  of  the  air,  and  consequently  diminishes 
only  in  a  trifling  degree  its  specific  gravity;  the  great  aerial  cur- 
rents formerly  described  as  pervading  the  atmosphere,  are  scarcely 
affected  by  the  vapour  they  contain. 

When  two  portions  of  vapour,  having  different  temperatures, 
are  mingled  together;  or  when  a  portion  of  vapour  is  brought  into 
a  state  of  mixture  or  contact,  with  a  portion  of  water,  or  with  any 
other  body  colder  than  the  vapour  ;  the  resulting  mean  tempera- 
ture, whatever  that  may  be,  is,  in  both  cases,  the  temperature  which 
regulates  the  elastic  force  of  the  mixture.  Now,  since  the  elastic 
force  of  vapour  increases  most  rapidly  from  the  temperature  of  32° 
to  212°,  the  increase  being  in  a  geometrical  progression,  while 
the  increase  of  the  temperature  is  in  an  arithmetical  progression; 
it  follows,  that  v/hen  two  portions  of  vapour  of  e([ual  bulk  but  of 
difl'erent  temperatures,  are  mixed  together  ;  or  when  a  portion  of 
vapour  is  brought  into  contact  with  any  solid  colder  body  ;  the 
resulting  mean  temperature  is  always  below  that  requisite  to  pre- 
serve the  water  in  a  state  of  vapour.  Hence,  such  mixture  or 
contact  is  always  followed  by  a  portion  of  the  vapour  being  con- 
densed into  water.     In  a  future  part  of  this  section,  it  will  be 


MIXED  ATMOSPHERE  OF  VAPOUR  AND  AIR.         165 

necessary  to  illustrate  further  this  important  fact,  but  a  familiar 
instance  may  be  noticed  here.  Let  us  suppose  that  a  pound  of 
water  at  tlie  temperature  of  212°,  which  being  in  a  state  of  steam, 
would  occupy  a  space  of  about  27  cubic  feet,  were  suddenly 
brought  into  mixture  with  a  pound  of  water  at  the  temperature  of 
32°:  the  effect  would  be  an  instantaneous  condensation  of  the 
greater  part  of  tiie  steam  into  water.  For  the  resuhing  mean  tem- 
perature would  obviously  be  far  short  of  212°,  below  which  tem- 
perature the  elastic  force  of  vapour  most  rapidly  diminishes.  On 
this  property  of  vapour  depends  the  working  of  the  common 
steam-engine. 

The  reader  is  thus  at  length  prepared  to  enter  on  the  compli- 
cated subject  of  a  mixed  atmosphere  of  vapour  and  of  air. 

We  have  shown  that  the  rate  of  decrease  of  the  temperature 
of  an  atmosphere  of  vapour,  in  ascending  from  the  earth's  surface, 
M^ould  be  very  much  slower  than  that  of  an  atmosphere  of  air. 
Now  since,  at  all  temperatures,  the  existence  of  atmospheric  air 
is  permanent  ;  while  the  very  existence  of  vapour  is  dependent 
on  temperature  ;  it  follows,  that  in  a  mixed  atmosphere  of  vapour 
and  of  air,  the  quantity  of  vapour  contained  in  the  mixture  is 
regulated  solely  by  the  temperature  of  the  air  :  that  is  to  say,  the 
quantity  of  vapour  present  in  an  aerial  atmosphere,  can  never  ex- 
ceed, though  it  may  be  less  than,  the  quantity  which  is  proper  to 
the  temperature  of  the  air.  If  the  quantity  of  vapour  in  such  a  mixed 
atnjosphere,  be  precisely  the  quantity  that  is  proper  to  the  tem- 
perature of  the  air,  such  an  atmosphere  is  said  to  be  saturated 
with  vapour. 

But,  neither  at  the  earth's  surface,  nor  at  any  height  above  if, 
can  the  degree  of  saturation  of  a  mixed  atmosphere  of  air  and 
vapour,  be  quite  equal  to  that  which  is  proper  to  the  temperature 
of  the  air  ;  and  the  difference  between  these  two  degrees  of  sa- 
turation, augments  from  above  downwards.  The  cause  of  this 
dilference  may  be  thus  explained.  The  rate  of  increase  of  the 
temperature  of  air,  from  above  downward,  being  in  arithmetical 
progression,  and  the  air  being,  in  a  mixed  atmospliere,  that  ingredi- 
ent M^iich  controls  the  whole  mixture;  the  rate  of  increase  of  the 
tension  of  the  vapour,  instead  of  following  the  geometrical  rate 
which  belongs  to  it  as  vapoin-,  is  obliged  to  conform  to  the  arith- 
metical rate  of  increase  of  the  temperature  of  the  air.  The  result 
of  this  controlment  necessarily  is,  that  the  quantity  of  vapour 
present  in  a  mixed  atmosphere  will,  at  any  successive  diminution 
of  the  height  above  the  surface  of  the  earth,  become  successively 
less  and  less  than  tliat  which  would  be  required  to  saturate  the 
air.     An  example  will  make  this  result  evident. 

At  the  Equator,  as  we  have  said,  the  temperature  of  the  air,  at 
the  height  of  about  15,000  feet,  above  the  level  of  the  sea,  is 
nearly  32°.     Now,   for  the  sake  of  illustration,  let  us  suppose 


166  METEOROLOGY. 

this  air  to  be  saturated  with  vapour.  From  Dr.  Dalton's  table  of 
the  tension  or  elastic  forces  of  vapour  at  different  temperatures, 
it  appears  that  the  tension  of  vapour  at  32°  is  equal  to  the  weight 
of  .200  inch  of  mercury  ;  and  that  the  difference  between  the 
tension  of  vapour  at  32°  and  the  tension  of  vapour  at  33°,  that  is 
to  say,  the  value  of  the  first  term  or  unit,  in  our  assumed  arithme- 
tical series  is  .007  inch  of  mercury.  Now,  the  difTerence  between 
32°  and  80°  the  mean  temperature  at  the  level  of  the  sea  under 
the  Equator,  is  48°  ;  and  supposing  each  of  these  48  degrees  to 
increase  in  an  arithmetical  progression,  .007  for  each  degree,  the 
tension  for  the  whole  48  degrees  will  amount  to  .336,  which 
added  to  .200,  the  tension  at  32°  gives  the  tension  of  .536  inch, 
as  that  corresponding  to  the  vapour  at  80°,  the  temperature  of  the 
earth's  surface  under  the  Equator.  But,  by  Dr.  Dalton's  same 
table  of  tensions,  we  find  that  .536  does  not  represent  the  proper 
tension  of  vapour  at  80°,  but  of  vapour  at  about  61°  only.  Ac- 
cording to  this  estimate  it  follows,  that  at  the  Equator,  while  the 
temperature  of  the  air  over  the  earth's  surface  is  80°,  the  point 
of  saturation  with  vapour  is  19°  below  that  temperature.  Hence, 
at  the  Equator,  the  air  immediately  incumbent  on  the  earth's  sur- 
face niust  be  comparatively  very  dry.  Moreover  the  cause  which 
has  been  thus  shown  to  produce  the  dryness  of  the  Equatorial 
air,  at  the  earth's  surface,  must  all  over  the  globe  exert  different 
degrees  of  the  same  influence.  The  air,  everywhere  incumbent 
on  the  earth'' s  surface,  must,  therefore,  always  be  under  the  point 
of  saturation  ; — the  relative  degree  of  dryness  being  highest  un- 
der the  Equator,  and  gradually  diminishing  as  we  recede  north  or 
south  towards  the  Poles.*' 

In  such  a  mixed  atmosphere  as  we  have  supposed,  and  as  in  reality 
surrounds  our  globe,  if  its  equilibrium  be  undisturbed,  and  if  it  be  at 
rest ;  the  vapour  it  contains  will  have  nearly  the  same  tendencies 
to  motion  and  to  dilTusion  that  would  exist  in  such  an  atmosphere 
of  pure  vapour,  as  we  have  formerly  described.  But  from  the 
more  equal  distribution  of  vapour,  when  mingled  with  air,  the  con- 
trasts between  the  specific  gravities  of  different  portions  of  vapour,  in 
different  parts  of  the  atmosphere,  will  be  much  less  striking  than 
if  the  atmosphere  consisted  of  vapour  alone.  Consequently,  the 
rates  of  motion  and  of  diffusion,  wliich  depend  upon  such  diff'er- 
ences  of  specific  gravity,  will  be  less  remarkable  in  a  mixed  atmo- 
sphere, even  though  saturated  with  vapour,  than  they  would  be 
in  a  purely  aqueous  atmosphere  ;   while  in  an  unsaturated  atmo- 

•  The  mathematical  reader  will  observe,  that  the  quantities  g-lven  in  the 
text  are  not  rigidly  accurate,  but  are  intended  only  for  flimiliar  illustration  I 
of  the  principles  reg-ulating'  moisture.  The  truth  is,  as  has  been  noticed 
hi  the  tvxt,  in  no  part  of  a  vertical  column  of  a  mixed  atmos])here,  in  a 
condition  of  equilibrium  and  at  rest,  can  the  air  be  in  a  state  of  saturation. 
It  has  been  remarked,  that  the  deg'ree  of  saturation  often  continues  nearly 
uniform  up  to  a  certain  point,  and  then  suddenly  decreases. 


MIXED  ATMOSPHERE   OF  VAPOUR  AND  AIR.  167 

Sphere  the  motions  of  the  vapour  must  be  still  more  liable  to  be 
influenced  by  the  motions  of  the  air,  than  they  would  be  in  an 
atmosphere  of  air,  at  its  utmost  point  of  saturation. 

Before  we  close  this  part  of  our  subject  let  us  reflect  for  a  mo- 
ment upon  the  consequences  of  such  a  stale  of  comparative  dry- 
ness of  the  lower  atmosphere  next  the  earth.     Over  the  greater 
portion  of  the  earth,   the   air  which,  during  the   day  at  least,  is 
warmed   by  contact  with  the  earth's  surface,  and  thus  becomes 
lighter,  has,  as   we  have  observed,  a  constant  tendency  to  rise 
into  the  higher  atmosphere.  Novv,  if  tliis  air  were  saturated  witli 
vapour,  of  course,  whenever  the  air  by  rising  became  mixed  with 
colder  air,  its  vapour  would  be  more  or  less  condensed,  and  a 
cloud  would  be  formed.     Hence,  if  we   lived   in   such   an   atmo- 
sphere, we  should  be  always  enveloped  in  a  mist,  through  which 
the  sun  would  not  be  visible.     Rut,  by  the  benevolent  arrange- 
ment we  enjoy,  this  consequence  is  so  entirely  prevented,   that, 
unless  under   peculiar   circumstances,   and  always   for    beneficial 
purposes,  the   air   at  the   earth's  surface  is  hardly  ever  saturated 
with  moisture.     The  air  that  has  been  warmed  by  contact  with 
the  earth  can,  therefore,  rise  from   the  surface,  without  any  con- 
densation of  its  nature  within  the  limits  of  its  point  of  saturation. 
Thus,  at  the  Equator,  before  the  air  reaches  the  temperature   of 
61°,  the  presumed  point  of  its   saturation,   it  must  ascend  to  the 
height  of  6000  or  7000  feet.     At  this  height  its  vapour  will   be 
condensed,   and  a  cloud  will  be  formed  ;   which   may  either  be 
precipitated  on  the  spot  from   which  its  constituent  vapour   had 
risen,  or  may  be  transported  by  the  currents  of  the  atmosphere, 
similarly  to  refresh  a  distant  country,  or  may  be  again  dissolved 
in  the  air ;   while  under  all  these   contingencies   the  whole  of  the 
lower  part  of  the  atmosphere  is  exempt  from  mist,  and  continues 
perfectly  transparent.     These  operations  are  unceasingly  carried 
on  in  our  atmosphere,  over  the  whole  surface  of  the  earth.   More- 
over, the  very  clouds,  by  giving  out  their  latent  heat,  and  shield- 
ing the  earth's  surface  from  the  direct  influence  of  the  sun,  pro- 
duce a  still  further  eff'ect,  and  have  a  constant  tendency  to  modify 
their  own  formation  and  existence. 

The  general  result  of  all  the  complicated  and  beautiful  ma- 
chinery connected  with  the  movement  of  vapour  is,  that  water  is 
incessantly  raised  into  the  higher  parts  of  the  atmospliere,  where 
it  is  again  condensed  in  the  form  of  rain,  &;c.  over  the  whole 
earth.  We  have,  therefore,  in  the  next  place  to  examine  a  little 
more  in  detail  the  relations  of  these  two  great  processes  of  evapo- 
ration and  condensation,  as  they  are  exhibited  in  nature. 

Of  the  general  Bclafions  of  Evaporation  and  condensation. — 
The  first  point  in  the  inquiry  that  naturally  claims  our  attention, 
are  the  rnechanical  motions  by  which  the  relations  between  eva- 
poration and  condensation  are  maintained. 


168  METEOROLOGY. 

The  motions  of  vapour,  in  a  mixed  atmosphere  of  vapour  and 
air,  may  be  considered  as  of  three  kinds  :  those  motions  arising  from 
convection,  in  which  the  vapour  is  carried  along  by  the  air  ;  those 
motions  arising  from  the  tendency  of  the  vapour  to  recover  its 
dynamical  (and  thermal)  equilibrium,  when  that  equilibrium  has 
been  disturbed,  and  which  motions  we  shall,  for  distinction,  term 
ihe  propei'  motions  of  the  vapour  ;  and  those  motions  of  vapour 
which  are  caused  by  diffusion. 

In  a  mixed  atmosphere  of  vapour  and  air,  the  motions  of  the  va- 
pour, on  the  large  scale  of  the  operations  of  nature,  are  influenced, 
no  doubt,  in  a  very  great  degree,  by  the  motions  of  the  air.  For 
example,  large  masses,  more  or  less  saturated  with  vapour,  in  pro- 
portion to  tiieir  respective  temperatures,  and  having  either  verti- 
cal or  lateral  motion,  must  carry  with  them  the  vapour  they  con- 
tain, whether  t.here  be  much  or  litUe  vapour  so  contained.  On 
the  other  hand,  motions  of  the  air,  on  a  smaller  scale,  as  we  shall 
presendy  see,  may  be  even  caused — may  certainly  be  accelerated 
or  retarded,  according  as  the  proper  motion  of  the  vapour,  to  be 
next  considered,  may  agree  with,  or  may  be  opposed  to,  these 
motions  of  the  air.  When  once,  however,  the  vapour  in  the  at- 
mosphere has  been  separated,  and  has  assumed  the  form  of  visi- 
ble vapour,  its  own  proper  powers  of  motion  cease,  and  it  be- 
comes entirely  subject  to  those  of  convection.  Visible  vapours, 
therefore,  of  all  kinds,  from  their  being  liable  to  be  wafted  by 
every  breeze,  are  in  a  constant  state  of  motion,  and  are  thus  fre- 
quently carried  where  vapour,  in  virtue  of  its  own  tendency  to 
motion,  would  never  reach. 

In  an  atmosphere  of  vapour,  when  the  temperature,  and  conse- 
quently the  elasticity,  of  any  portion  is  reduced  ;  the  surrounding 
vapour,  by  virtue  of  its  greater  elastic  force,  continues  to  advance 
towards  the  cooler  locality  and  to  be  there  condensed  until  the 
thermal  equilibrium  is  restored.  'i"he  motion  thus  arising,  which 
depends  upon  its  dynamical  properties,  constitutes  what  we  have 
denominated  \\ic  proper  motion  of  vapour.  In  an  atmosphere  of 
vapour  this  restoration  of  the  dynamical  equilibrium,  upon  which 
the  tliermal  equilibrium  also  depends,  would  take  place  with  so 
great  rapidity,  as  to  be  almost  instantaneous.  But  in  a  mixed 
atmosphere,  the  case  is  dilTerent.  In  such  an  atmosphere,  the 
presence  of  the  heavier  and  more  abundant  air  modifies,  in  a  re- 
markable degree,  the  rapid  motion  of  t!ie  lighter  and  less  abun- 
dant vapour.  Hence,  instead  of  a  rush  of  vapour  and  a  momen- 
tary deluge,  the  motions  of  the  vapour  take  place  slowly  ;  and 
sudden  evaporation  and  condensation,  with  their  consequences,  are 
efTectuully  prevented. 

These  tendencies  to  motion,  in  vapour  of  difierent  tempera- 
tures, have,  no  doubt,  great  influence  on  the  contiguous  surfaces 
of  large  masses  of  air  dilTerenily  saturated  ;   and,  in   particular, 


MIXED  ATMOSPHERE  OP   VAPOUR  AND  AIR.         169 

are  liable  to  affect  smaller  masses  of  air  differently  saturated, 
when  they  are  in  the  immediate  neighbourhood  of  each  other. 
Thus,  as  we  have  already  noticed,  the  disturbance  of  the  equili- 
brium of  the  vapour  may  be  to  such  an  extent,  in  some  portion  of  the 
mixed  atmosphere  ;  that  the  surrounding  vapour,  urged  to  move 
by  its  tendency  to  restore  the  equilibrium,  may  occasionally  be 
supposed  to  drag  with  it  the  air  and  the  clouds,  and  thus  produce 
local  currents.  For  instance,  let  us  imagine  a  mass  of  warm  and 
almost  perfectly  dry  air  to  be  brought  into  the  neighbourhood  of 
another  mass  of  air  of  precisely  the  same  temperature,  but  satu- 
rated with  vapour.  The  two  masses  of  air,  from  being  of  the 
same  temperature,  would,  as  air,  have  no  tendency  to  intermingle. 
But  as  being  portions  of  a  mixed  atmosphere  of  vapour  and  air, 
the  dryer  air  would  be,  as  it  were,  a  vacuum,  towards  which  the 
vapour  from  tlie  moist  air  would  have  a  tendency  to  flow  till  both 
masses  of  air  became  equally  moist.  In  such  a  case,  the  motion 
of  the  vapour  might  be  supposed  to  cause  more  or  less  of  motion 
in  the  air,  while  a  momentary  cloud  would  probably  be  formed  ; 
which  cloud  would  be  dissipated  when  the  equilibrium  was  re- 
stored. In  this  way,  it  is  likely  that  many  of  the  minor  motions 
of  the  atmosphere  are  produced."^ 

The  motions  of  vapour  arising  from  its  diffunive  powers  are 
quite  distinct  from  those  motions  of  vapour  which  are  controlled 
by  the  motions  of  the  air,  or  by  die  dynamical  tendencies  of  the 
vapour  itself  to  recover  its  condition  of  thermal  equilibrium. 
These  diffusive  motions  of  vapour,  as  formerly  observed,  depend 
on  differences  between  the  specific  gravities  (the  absolute  quanti- 
ties of  matter)  of  contiguous  and  communicating  gases,  under  the 
same  circumstances  of  pressure  and  temperature.  Though  the 
motions  of  vapour  depending  on  diffusion  may  retard,  or  be  re- 
tarded by,  the  other  motions  to  which  vapour  is  liable  ;  in  gene- 
ral, there  is  reason  to  believe  that  the  motions  of  vapour  by 
diffusion,  in  their  most  decided  form,  surpass,  or  take  place  in- 
dependently of,  all  the  other  motions  of  vapour,  and  in  this  free- 
dom from  control,  resemble  the  radiation  of  imponderable  bodies. 
The  laws  which  diffusion  obey  have  been  already  stated,  and 
need  not  be  again  repeated.  These  laws  may  be  applied  to  the 
consideration  of  the  diffusion  of  vapour  in  the  following  manner. 

The  diffusive  tendencies  of  an  atmosphere  of  perfectly  dry  air, 
and  of  an  atmosphere  of  vapour,  would,  as  we  have  seen,  at  the 
earth's  surface  be  in  opposite  directions  ;  the  diffusive  tendency 
in  the  aerial  atmosphere,  being  from  the  Equator  toward  the 
Poles,  and  that  in  the  aqueous  atmosphere  being  from  the  Poles 

*  In  all  the  cases  given  in  the  text,  the  effect  of  electricity  is,  for  the 
sake  of  distinctness,  kept  out  of  view. 

15 


170  METEOROLOGY. 

towards  the  Equator.  The  vertical  tendencies  also  of  the  two  atmo- 
spheres would  be  very  different.   An  atmosphere  of  perfectly  dry 
air,  in  astate  of  thermal  and  dynamical  equilibrium,  would  have  no 
tendency  to  diffusion  ;  for  the  colder  air  in  descending,  and  the 
warmer  air  in  ascending,  by  change  of  bulk,  acquire  the  temperature 
appropriate  to  the  height.     The  effect  of  this  change  of  bulk  and 
acquisition  of  temperature  is,  as  we  have  elsewhere  stated,  such, 
that  if  air  from  any  height  in  the  atmosphere  were  brought  to  the 
surface  of  the  earth,  it  would  have  precisely  the  same  tempera- 
ture as  the  air  already  incumbent  on  the  surface.     But  the  case  is 
different  with  vapour,  even  in  the  comparatively  rare   state   in 
which  it  exists  in  a  mixed  atmosphere.     We  have  seen  that  in 
an  atmosphere  of  vapour,  if  the  temperature  at  the  surface  of  the 
earth  were  80°,  the  temperature  at  the  height  of   15,000  feet 
would  be  only  70°  ;  while  in  an  atmosphere  of  perfectly  dry  air, 
having  a  similar  surface  temperature  of  80°,  the  temperature,  at 
the  same  height  of  15,000  from  the  surface,  would  be  32°.    Now, 
as  in  a  mixed  atmosphere  of  vapour  and  air,  the  temperature  of 
the  air  determines  that  of  the  vapour  ;   if  in  such  a  mixed  atmo- 
sphere, vapour  having  the  temperature  of  32°,  were  brought  from 
the  height  of  15,000  feet  to  the  surface,  where  the  temperature 
is  80°  ;  the  temperature  of  the  vapour  would,  by  increased  pres- 
sure and  the  consequent  evolution  of  more  latent  heat,  be  in- 
creased only  to  about  42°  ;  while,  as  we  have  seen,  where  the 
temperature  of  the  surface  is  80°,  the  point  of  saturation  of  the 
air  with  vapour  is  at  least  61°.     Hence  the  specific  gravity  of 
vapour  from  the  height  of  15,000  feet,  when  reduced  to  the  same 
degree  of  pressure  as  that  at  the  surface,  is  found  to  be  much  be- 
low  the  specific  gravity  of  that  vapour  which  actually  exists  at 
the  surface.     Consequently,  throughout  a  mixed  atmosphere  of 
vapour  and  air,  tliere  is  a  tendency  to  vertical  diffusion,  the  pre- 
dominant tendency  being  from  above   downwards.     From   the 
extreme   tenuity  of  vapour   in  the  higher  regions  of  the    atmo- 
sphere, and  the  great  tendency  therefore,  which  that  vapour  has 
to  diffusion,  it  is  probable  that  the  diffusive  motion  of  the  vapour 
may  occasionally  have  a  velocity  approaching,  as  we  have  said, 
to  that  of  radiant  matter,  itself.     In  this  way  the  rare  and  cold 
molecules  of  water  may  be  supposed   to  dart,  or  radiate,  as  it 
were,  far  into  the  warmer  atmosphere  before  their  velocity  is  ar- 
rested.    Nay,  in  the  Polar  latitudes,  the  molecules  of  water,  from 
the  higher  parts  of  the  atmosphere,  may  even  reach  the  earth's 
surface,  by  shooting,  like  rays  of  heat  and  light,  directly  through 
the  air,  without  materially  affecting  its  temperature. 

After  these  general  remarks  on  the  motions  of  vapour,  we  shall 
now  take  a  rapid  view  of  the  mutual  relations  of  the  two  great  pro- 
cesses of  evaporation  and  condensation. 


EVAPORATION  AND  CONDENSATION,  MUTTJAL.  171 

We  have  already  described  the  general  phenomena  of  evapora- 
tion and  condensation,  and  have  slated  llie  laws  on  which  these 
phenomena  depend.  It  will,  tlierefore,  in  this  place,  be  sufficient 
to  remind  the  reader  that  the  degree,  and  the  rate,  of  evaporation 
though  they  increase  with  the  temperature,  are  regulated  chiefly 
by  the  existing  degree  of  saturation  of  the  air.  That  is  to  say, 
under  all  temperatures  evaporation  decreases,  as  the  air  that  re- 
ceives the  vapour,  approaches  its  point  of  saturation.  Hence  it 
follows,  that  in  an  atmosphere  perfectly  saturated  with  moisture, 
and  in  a  state  of  thermal  and  dynamical  equilibrium,  there  can  be 
neither  evaporation  nor  condensation.  The  processes  of  evapo- 
ration and  condensation,  therefore,  always  indicate  a  disturbance 
of  the  thermal  equilibrium  in  some  part  of  the  atmosphere  :  con- 
densation denoting  a  depression  of  tlie  temperature  below  the  mean, 
or  point  of  thermal  equilibrium:  evaporation,  on  the  contrary,  de- 
noting that  the  temperature  in  some  part  of  the  atmosphere  has 
been  raised  above  the  mean  ;  or  at  least  that  the  temperature  having 
been  depressed  below  the  mean,  is  again  undergoing  an  elevation 
to  the  mean  point.  Evaporation  and  condensation  may  be  thus 
considered  as  mutually  dependent ;  so  that  one  process  cannot 
take  place  without  the  other.  For  this  reason,  in  the  great  expanse 
of  nature,  these  two  processes  oscillate  or  fluctuate  about  the  point 
of  equilibrium,  within  certain  limits  which  are  never  passed  ;  and 
which  limits,  though  subject  to  countless  anomalies,  in  general, 
decrease  from  the  Equator  toward  the  Poles. 

With  respect  to  the  temperature  which  constitutes  the  point  of 
equilibrium  ;  in  an  atmosphere  of  vapour,  that  point  would,  of 
course,  be  the  maximum  point  of  saturation.  But  in  a  mixed  at- 
mosphere of  vapour  and  air  like  that  of  our  globe,  the  point  of 
equilibrium  cannot  be  the  point  of  utmost  saturation,  but  must  be 
that  inferior  point  of  saturation  formerly  described,  as  being  de- 
termined by  the  temperature  of  the  predominant  air.  Thus  at 
the  Equator,  where  the  mean  temperature  at  the  level  of  the  sea 
is  about  80°,  the  mean  point  of  saturation  will,  according  to  our 
former  estimate,  be  61°  ;  while  in  London,  where  the  mean  annual 
temperature  is  about  49^°,  the  mean  point  of  saturation,  (or  the 
deiv  pointy  as  it  is  termed,)  has  been  fixed  by  Mr.  Daniell  at  445°. 
In  temperate  climates,  the  mean  point  of  saturation  at  any  particu- 
lar place,  varies  with  the  seasons  from  day  to  day,  being  higher 
in  summer  than  in  winter.  During  any  shorter  period,  as  that  of 
a  day  and  night,  the  mean  point  of  saturation,  as  might  be  ex- 
pected, generally  bears  a  certain  relation  to  the  lowest  degree  to 
which  the  ten^iperature  has  fallen  during  the  period  ;  since  the 
Hygrometer^  shows  that  the  degree  of  saturation,  at  any  hour,  is 

*  The  Hygrometer  is  an  instrument  for  measuring'  the  degree  of  m-ois* 


172  METEOROLOGY. 

seldom  below  the  point  of  saturation  corresponding  to  tlie  lowest 
temperature  of  the  twenty-four  hours  ;  at  which  point  it  continues 
nearly  uniform,  so  that  the  point  of  saturation  during  the  warmer 
parts  of  the  day  generally  varies  only  a  few  degrees.  The  ele- 
vation and  depression  of  the  dew  point  in  temperate  climates  is 
thus  another,  and  unceasing  cause  of  change,  and  produces  a  va- 
riety in  evaporation  and  condensation  so  great  as  to  baffle  any  at- 
tempt at  accurate  inquiry. 

From  what  has  been  said,  it  will  appear  that  in  a  mixed  atmo- 
sphere, the  rate  of  evaporation  and  of  condensation,  other  things 
being  equal,  will  depend,  not  on  the  ditlerence  of  the  tempera- 
ture of  the  air  from  the  maximum  point  of  saturation,  but  on  the 
difference  of  the  temperature  of  the  air  from  that  of  the  mean  dew 
point ;  that  is  to  say,  will  increase  or  diminish  as  this  difference 
increases. 

The  accidental  circumstances  which  principally  operate  to  af- 
fect the  rate  of  evaporation,  are  the  greater  or  less  extent  of  the 
evaporating  surface,  and  the  velocity  and  degree  of  saturation  of 
the  current  of  air  over  that  surface.  But  besides  these  causes  of 
variation,  there  are  other  circumstances  wliich  probably  have  great 
influence  on  evaporation ;  some  of  which  are  to  us  of  the  utmost 
interest,  as  being  brought  more  immediately  in  contact,  as  it  were, 
with  our  existence.  The  chief  of  these  additional  circumstances 
affecting  evaporation  which  we  shall  notice,  are.  Diffusion; — 
Circumstances  incidental  to  the  IVater  which  undergoes  evapo- 
ration ;  and  Circimistances  incidentcd  to  the  Air  into  which  the 
water  is  evaporated. 

By  the  general  arrangement  which  we  formerly  considered,  it 
appears  that  evaporation  and  condensation  diminish  from  the  Equa- 
tor, onward  to  the  Poles.  But  since  increased  temperature,  which 
is  the  cause  of  evaporation,  predominates  at  the  Equator;  while 
diminished  temperature,  which  is  tire  cause  of  condensation,  pre- 
dominates at  the  Poles  ;  it  may  perhaps  be  inferred,  that  generally 
speaking,  evaporation  will  be  relatively  greater  at  the  Equator;  and, 
on  the  other  hand,  that  condensation  will  be  relatively  greater  at 
the  Poles.  In  an  atmosphere  of  vapour  such  unequal  effects  could 
not  indeed  take  place  ;  from  the  rapid  nature  of  the  motions  which 
would  arise  throughout  the  whole  of  such  an  atmosphere,  so  as 
instantaneously  to  restore  the  equilibrium.  But  in  a  mixed  atmo- 
sphere of  vapour  and  air,  the  result  would  be  different.  If  there 
were  an  excess  of  condensation  at  the  Poles  ;  before  the  corre- 


ture  of  the  atmosphere.  That  of  Mr.  Daniel!  is  here  alluded  to,  which  is 
the  only  one  that  acts  upon  scientific  principles.  Danicll's  hygrometer 
shows  the  degree  of  temperature  at  which  water  is  deposited  from  the  at- 
mosphere, and  consequently  its  state  of  saturation. 


EVAPORATION  AND  CONDENSATION,  MUTUAL.  173 

sponding  evaporation  could  take  place  at  the  Equator,  innumerable 
changes  would  be  produced  in  the  atmospliere  over  all  the  other 
parts  of  the  globe  intervening  between  the  Equator  and  the  Poles. 
Further,  we  shall  see  presently  that  much  more  water  is  at  all 
times  condensed  on  the  land,  than  is  ever  evaporated  from  the  land. 
The  excess  that  is  condensed  flows  off  in  rivers  in  warm  and  tem- 
perate climates,  and  thus  accumulation  is  prevented  ;  but  in  the 
Polar  regions  this  outlet  is  cut  off,  and  the  superfluous  water  would 
be  locked  up  in  the  shape  of  ice.  From  these  circumstances, 
therefore,  and  from  others  that  might  be  noticed,  it  is  not  unreason- 
able to  suppose,  that  in  the  colder  climates,  other  things  being 
alike,  and  the  arrangements  which  regulate  vapour  being  alone 
considered,  condensation  of  water  would  proceed  much  more  ra- 
pidly than  its  evaporation  ;  and  hence  that  around  the  Poles  there, 
would  be  a  constant  accumulation  of  water  in  the  condition  of  ice. 
But  we  know  that  there  is  not  any  such  accumulation,  in  those 
parts  of  the  Polar  regions  which  have  been  explored.  It  is  mani- 
fest, therefore,  that  in  these  regions  the  energy  of  evaporation 
must  be  fully  equal  to  that  of  condensation.  It  is  indeed  true, 
that  evaporation  goes  on  very  rapidly  from  snow  and  ice.  Thus 
Howard  mentions  an  instance  in  the  month  of  January,  in  a  cer- 
tain year,  when  the  vapour,  from  a  circular  area  of  snow  five  inches 
in  diameter,  amounted  to  150  grains  between  sunset  and  sunrise; 
and  before  the  next  evening,  50  grains  more  were  added  to  the 
amount,  the  gauge  having  been  exposed  to  a  smart  breeze  on  the 
housetop.  Under  like  circumstances  an  acre  of  snow  would,  in 
the  course  of  twenty-four  hours,  evaporate  the  enormous  quantity 
of  64,000,000  grains  of  moisture  !  Even  by  the  evaporation  du- 
ring the  night  only,  a  thousand  gallons  of  water  would,  in  that 
short  time,  be  raised  from  an  acre  of  snow.  It  may  thus  be  easily 
understood  how  a  moderate  fall  of  snow  may  entirely  vanish  du- 
ring a  succeeding  northerly  gale,  without  the  slighest  perceptible 
liquefaction  on  the  surface.* 

We  have  given  this  statement  to  satisfy  the  general  reader  of 
the  fact,  that  evaporation  is  constantly  going  on  from  snow  and 
ice.  But  the  quantity,  great  as  it  appears,  does  not  surpass,  or 
even  equal,  what  it  might  be  supposed  to  be,  on  admitted  princi- 
ples. Whether,  thereiore,  evaporation  really  takes  place  in  a  re- 
latively greater  degree  in  the  Polar  regions,  so  as  to  compensate 
for  that  portion  of  the  condensed  water  which  is  there  fixed  as 
ice,  but  which  in  warmer  climates  flows  off  to  the  sea,  in  the 
form  of  rivers,  remains  to  be  proved  ;  though,  to  preserve  the 
equilibrium  and  to  prevent  accumulations,  some  such  supposition 
appears  to  be  necessary.     Can  the  difficulty  be  solved  by  the  aid 

•  Article  Meteorology  in  the  Encyclopedia  Metropolitana. 

15* 


174  METEOROLOGY. 

of  the  principles  of  diffusion  ?  Does  not  a  portion  of  the  attenu- 
ated vapour  of  the  Polar  latitudes  difl'use  itself,  and  penetrate 
from  thence  towards  the  Equator  ;  thus  leaving  the  higher  re- 
gions of  the  atmosphere  in  the  Polar  latitudes  comparatively  dry, 
and  the  lower  portion  of  the  atmosphere  more  apt  for  evaporation  ? 
And  is  not  this  diffusion  of  moisture  from  the  Poles  one  of  those 
beautiful  expedients,  which  compensate  for  the  inequalities  of 
evaporation  and  condensation,  and  by  which  these  inequalities 
are  obviated  ? 

The  circumstances  incidental  to  ivater,  and  affecting  evapora- 
tion and  saturation,  arise  chiefly  from  its  purity  or  impurity. 
The  presence  of  foreign  bodies,  as  of  saline  matters,  for  instance, 
is  well  known  to  raise  considerably  the  boiling  point  of  water  ; 
in  other  words,  they  lower  its  tendency  to  become  vapour,  and 
thus  diminish  its  evaporating  and  saturating  powers.  Hence  the 
air  over  the  sea,  though,  of  course,  much  nearer,  in  general,  to 
the  point  of  saturation  appropriate  to  the  latitude  and  temperature, 
than  air  over  the  land,  is  comparatively  seldom  in  a  state  of  per- 
fect saturation  ;  and  sea-water,  so  far  from  being  capable  of  satu- 
rating the  air  with  moisture,  up  to  the  dew  point,  has  even  the 
power  of  abstracting  a  portion  of  the  moisture  from  an  atmo- 
sphere so  saturated,  and  of  thus,  to  a  certain  extent,  drying  the 
air. 

Evaporation  on  land  is  precisely  similar  to  evaporation  from 
sea-water,  since  the  various  rocks  and  soils  may  be  considered  as 
so  many  saline  matters,  diminishing,  in  their  several  degrees,  the 
tendency  to  become  vapour  possessed  by  the  water  united  with 
them.  Hence,  under  like  circumstances,  some  rocks  and  soils 
are  dry,  while  others  are  moist ;  so  that,  in  proportion  to  the 
evaporating  powers  of  the  rocks  and  soil  of  a  country,  will  that 
country  be  liable  to  all  the  consequences  of  dryness  or  of  damp- 
ness of  soil.  Plants  also  seem  to  differ  much  in  their  capacity 
for  retaining  water.  The  dryness  of  a  country  will,  therefore, 
be  considerably  affected  by  the  nature  of  its  vegetation  ;  and  the 
predominance  of  certain  plants  or  trees  in  a  district  may  thus  in- 
crease the  dampness  of  its  soil. 

Regarding  the  effect  that  foreign  matters  in  the  atmosphere 
have  in  influencing  evaporation  from  the  subjacent  land  or  water, 
we  are  unable  to  speak  with  as  much  confidence,  as  we  have 
spoken  of  the  controlling  power  of  the  foreign  matters  in  the  water 
iiself.  Many  years  ago,  particular  circumstances  led  us  to  form 
the  opinion,  that  a  combination  of  water  and  oxygen  is  a  frequent, 
if  not  a  constant,  ingredient  in  the  atmosphere.  This  ingredient, 
which  we  suppose  to  be  a  vapour,  and  analogous  to  (we  do  not 
say  identical  with)  the  deutoxide  of  hydrogen,  may  be  the  cause 
of  numerous  atmospheric  phenomena,  which  at  present  are  very 


EVAPORATION  AND  CONDENSATION,  MUTUAL.  175 

little  understood.     Among  such  phenomena  are  those  of  evapo- 
ration we  are  now  considering. 

The  dilhcullies  attending  an  investigation  of  the  atmosphere, 
and  more  than  all,  the  total  want  of  opportunity,  have  rendered  us 
unable  satisfactorily  to  verify  the  opinion  we  have  advanced. 
We  have  stated  the  opinion  as  conjectural  only,  and  in  order  that 
the  attention  of  those  more  fortunately  situated  may  be  drawn  to 
so  important  an  inquiry. 

When  treating  of  the  composition  of  atmospheric  air,  we  ob- 
served that  the  best  analyses  almost  invariably  indicated  a  slight 
excess  of  oxygen  above  the  amount  of  20  per  cent,,  which 
there  ought  to  be  in  the  atmosphere,  if  its  composition  were,  as 
there  can  be  little  doubt  that  it  is,  determined  by  the  laws  of  che- 
mical proportions.  Now  this  excess  of  oxygen  in  the  atmosphere, 
we  have  every  reason  to  think,  becomes  periodically  associated 
in  some  way  with  the  vapour  that  is  also  in  the  atmosphere  ;  and 
thus  not  only  modities  the  properties  of  the  vapour,  but  at  the 
same  time  materially  influences  the  rate  of  evaporation  from  the 
earth's  surface.  This  excess  of  oxygen  may  operate  in  the  fol- 
lowing manner.  The  vapour  in  union  with  oxygen  (deutoxide 
of  hydrogen?)  ceases,  of  course,  to  act  as  vapour;  hence  in  air 
saturated  with  vapour,  and  as  moist  as  possible,  if  a  portion  of  the 
vapour  were  suddenly  to  combine  with  oxygen,  the  air  would  as 
suddenly  appear  to  become  dry,  though  in  reality  it  contained  the 
same  quantity  of  water  in  solution  as  before.  Moreover  the  rate  of 
evaporation  would  be  increased  by  such  a  combination  of  vapour  and 
oxygen  ;  for  its  efiects,  whatever  these  might  be,  would  be  super- 
added to  the  ordinary  eflects  of  evaporation,  and  would  thus  more 
or  less  increase  the  quantity  of  water  converted  into  vapour. 

Oxygen  in  this  state  of  combination  with  vapour  seems  to  be 
particularly  grateful,  if  not  necessary  to  animal  life.  The  air  in 
which  it  abounds  is  dry,  bracing,  and  exhilarating,  while  the  pre- 
dominance of  moisture,  from  its  occasional  and  sudden  abstraction, 
induces  the  opposite  feeling  of  dulness  and  listlessness.  It  is 
probable  that  some  soils  and  situations  are  more  favourable  than 
others  to  its  existence,  and  that  places  are  more  or  less  healthy 
according  as  it  is  present  or  absent. 

The  oxygen  and  vapour  in  this  combination  are  so  feebly  as- 
sociated that  they  appear  to  be  separated  by  the  slightest  cause. 
Hence  the  results  of  every  common  analysis  and  examination  of 
air  are  the  same  nearly  as  if  such  a  state  of  combination  did  not 
exist.  We  may  mention,  however,  as  corroborative  of  our  opi- 
nion, the  bleaching  qualities  of  dew  and  of  the  air  itself,  as  also 
the  large  proportion  of  oxygen  sometimes  contained  in  snow  wa- 
ter and  in  rain  water  ;  attention  being  at  the  same  time  directed  to 
the  well  known  bleaching  qualities  of  the  deutoxide  of  hydrogen. 

Much  more  might  be  said  on  this  curious  subject,  especially 


176  METEOROLOGY. 

regarding  its  relation  to  the  electricity  of  the  atmosphere.  But 
as  our  observations  must  be  in  some  measure  speculative  we  shall 
for  the  present  desist. 

Of  the  actual  Quantity  of  Water  that  is  evaporated  and  con- 
densed over  the  Globe. — From  the  principles  we  have  stated  it 
will  appear  that  the  quantity  of  water  evaporated  and  condensed 
over  the  globe  may  be  supposed  to  vary  with  the  mean  temperature, 
and  consequently  with  the  latitude.  But,  from  local  or  other 
causes,  the  quantity  varies  so  much,  even  in  the  same  place,  in 
different  years,  that  the  exceptions  are  more  numerous  than  the 
instances  of  the  correctness  of  the  rule. 

The  following  table,  however,  shows  the  general  truth  of  the 
supposition,  and  that  the  average  quantity  of  rain  diminishes  from 
the  Equator  to  the  Poles.  In  fact,  a  much  larger  quantity  of  rain 
must  fall  in  the  Equatorial  than  in  the  Polar  regions,  as  is  suffi- 
ciently proved  by  the  magnitude  of  the  rivers  within  the  Tropics ; 
for  the  size  of  the  rivers  of  course  depends  on  the  quantity  of  the 
rain  ;  the  rivers  being  the  conduits  along  which  a  certain  portion 
of  the  precipitated  water  is  borne  to  the  sea. 

TABLE. 

Inches. 

Uleaborg            _..._.-  13.5 

Petersburg  -  -  -  -  -  -  16,  17.5 

Paris                   19.9 

London *20.7, 122.2, +25.2 

Edinburgh 22.,  24.5,  §26.4 

Mean  of  Carlsruhe,  Manheim,  Stuttg-ard,  Wurtzburg",  Augsburg, 

and  Ptegensburg,  (Schow)           ....             -  25.1 

Epping                ...                         ...  27.0 

Bristol 29.2 

England  (Dalton's  mean)          -             -             -             -             -  31.3 

Liverpool    -..-----  34.1 

Manchester       .....--  36.1 

Rome           ...             .....  39.0 

Lancaster         -             ..-.--  39.7 

Geneva         ....--.-  42.6 

Penzance           .....--  44.7 

Kendal         ....-.--  53.9 

Mean  of  twenty  places  in  the  lower  valleys  at  the  base  of  the  Alps  58.5 

Great  St.  Bernard          ......  63.1 

Vera  Cruz                -        .     -            -            -            -            -            -  63.8 

Keswick             .......  67.5 

Calcutta       -             -             -             -             -             -             -             -  81.0 

Bombay               .......  82.0 

Ceylon         ....----  84.3 

Adam's  Peak,  ditto       ..-.--  100. 

Coast  of  Malabar    -------  123.5 

I.,cogane,  St.  Domingo               .             .            -             -             -  150.[1 

*  Dalton.  t  Danicll.  i  Howard.  §  Adie. 

H  From  the  Encyclopaedia  Metropolitana.  Article  Meteorology,  p.  123, 


QUANTITY  EVAPORATED  AND  CONDENSED.         177 

In  this  table  the  names  of  the  places  to  which  it  refers  are 
arranged  progressively,  according  to  the  amount  of  rain  that  falls 
in  each  place  ;  and  though  the  progression  exhibits  great  irregu- 
larities, yet  the  table  fully  establishes  the  general  decrease  of  rain 
with  the  increase  of  distance  from  the  Equator. 

Sir  John  Leslie  has  shown  that  if  all  the  aqueous  vapour  which 
can  at  any  time  be  held  in  solution  by  the  whole  atmosphere, 
were  at  once  precipitated  on  the  earth  in  the  form  of  rain,  it  would 
not  be  more  than  about  five  inches  in  depth :  now  as  in  the  course 
of  a  year  many  times  this  quantity  of  rain  falls  from  the  atmo- 
sphere, its  replenishment  of  course  must  depend  upon  evapora- 
tion; of  which  evaporation  we  may  thus  infer  the  general  amount. 
With  respect  to  the  quantity  of  rain  that  descends  annually  on 
the  entire  surface  of  the  earth,  we  want  the  means  of  forming  an 
estimate,  though  tjiere  is  no  proof  that  this  quantity  is  subject  to 
any  material  diflerence.  The  distribution  indeed,  as  we  have 
seen,  diminishes  with  the  latitude,  and  varies  according  to  nume- 
rous local  peculiarities,  to  some  of  which  we  shall  hereafter  allude. 
Often  also,  no  doubt  for  the  wisest  purposes,  the  same  place  is 
liable  to  considerable  fluctuations  in  the  annual  amount  of  rain, 
or  at  least  in  the  times  of  its  precipitation ;  yet  all  these  variations 
oscillate  within  certain  limits,  and  scarcely  afTect  the  mean  quan- 
tity proper  to  the  place ;  thus  showing  that  the  distribution  of 
rain  obe3's  the  same  laws  that  regulate  the  more  general  and  fixed 
operations  of  nature. 

Of  the  whole  water  that  is  condensed  upon  the  surface  of  the 
earth,  a  certain  portion,  of  course,  enters  into  the  soil.  The 
depth  to  which  such  water  sinks  is  determined  by  the  declivity 
of  the  surface,  by  the  nature  of  the  inferior  strata,  and  by  other 
circumstances  ;  but,  after  a  greater  or  less  period,  and  range  of 
circulation,  it  usually  again  makes  its  appearance  in  the  open  day, 
in  the  form  of  Springs.  The  conjunction  of  springs  and  the  oc- 
casional addition  of  a  portion  of  rain  water,  which  is  neither  im- 
mediately absorbed  by  the  soil,  nor  evaporated,  constitute  brooks 
and  rivulets  ;  these  again  uniting  in  their  progress  from  the  higher 
and  interior  parts  of  the  countries  where  this  water  has  been 
deposited,  form  the  larger  rivers,  which,  after  dispensing  innu- 
merable benefits  to  the  inhabitants  of  the  plains  in  their  course, 
finally  discharge  their  superfluous  waters  into  the  ocean.  As  the 
origin  of  the  superfluous  water  which  flows  from  the  rivers  to  the 
ocean  is  thus,  unquestionably,  derived  from  the  vapour  condensed 
in  the  interior  of  the  countries  where  the  rivers  originate,  it  fol- 
lows, that  in  every  country  where  there  are  rivers,  condensation 
must  surpass  evaporation.  That  is  to  say,  a  large  proportion  of 
water  condensed  on  the  land,  must  have  been  evaporated  not  from 
the  land,  but  from  the  neighbouring  ocean. 


178  METEOROLOGY. 

The  relative  proportions  of  the  water  that  is  condensed,  and  of 
the  water  that  is  evaporated  vary  exceedingly  in  different  countries. 
Such  indeed  is  the  amount  and  variety  of  the  differences  that  it  is 
impossible  to  estimate  them  ;  though  it  is  probable  that  in  the  same 
country  the  proportions  are  nearly  constant ;  or,  at  least,  that  there 
is  a  mean  proportion  about  which  the  differences  oscillate  within 
trifling  limits.  In  this  country,  Dr.  Thomson  has  estimated  that, 
taking  the  whole  of  Great  Britain  together,  the  mean  fall  of  rain 
amounts  in  the  course  of  a  year  to  3G  inches,  the  dew  being  in- 
cluded, (which  is  considered  to  amount  to  about  four  inches)  ;  and 
that  the  quantity  of  water  evaporated  is  about  32  inches.  Conse- 
quently, the  excess  of  four  inches  must  be  supposed  to  go  to  sup- 
ply the  springs  and  rivers  :  and  as  these  four  inclies  are  thus  not 
taken  up  again  by  evaporation  from  the  land,  they  must  be  drawn 
from  the  seas  that  encircle  our  shores.*  These  estimates  of  the 
water  that  is  condensed  and  evaporated  in  Great  Britain  can  only 
be  viewed  as  rude  approximations  ;  and,  even  admitting  them  to 
be  correct,  they  could  scarcely  be  applied  with  any  advantage  to 
an  inquiry  into  the  actual  condensation  and  evaporation  in  other 
countries  or  climates,  which  in  all  instances  must  be  determined 
by  observation  and  experiment. 

Having  spoken  of  the  accidental  circumstances  which  influence 
evaporation,  we  are  now,  in  the  last  place,  to  treat  of  those  acci- 
dental circumstances  which  injiuence  condensation. 

The  condensation  of  vapour  fi'om  the  atmosphere,  as  we  have 
already  stated,  differs  in  some  degree,  according  to  the  origin  of 
that  diminished  temperature  by  which  the  condensation  is  pro- 
duced. We  shall,  therefore,  commence  with  the  phenomena  of 
the  precipitation  of  moisture  depending  on  the  radiation  of  heat 
from  the  earth's  surface  ;  the  most  remarkable  of  these  phenomena 
are  Dew,  Hoar  Frost,  and  certain  forms  of  Mist, 

Of  Dew. — The  phenomena  of  dew  were  flrst  satisfactorily  ex- 
plained by  the  late  Dr.  Wells,  who  showed  by  the  most  decisive 
experiments  that,  apparently,  they  were  all  owing  to  the  effects 
of  the  radiation  of  heat  from  the  earth's  surface  into  space,  during 
the  absence  of  the  sun.  The  reader  is  referred  to  Dr.  Well's  "  Es- 
say on  Dew'^  for  details.  It  is  suflficient  for  our  present  purpose 
to'observe,  that  when  the  direct  influence  of  the  sun  is  removed 
in  the  evening,  and  the  surface  of  the  earth  thus  no  longer  conti- 
nues to  acquire  heat;  at  that  instant,  from  the  ceaseless  activity 

•  On  heat  and  electricity,  p.  266.  It  Is  proper  to  observe,  that  this  es- 
timate differs  considerably  h-ooi  a  previous  estimate  of  Dr.  Dalton,  who 
fixes  the  proportion  of  water  as  flowinj^  ofl'by  the  rivers,  in  Eng-land  and 
Wales,  at  thirteen  inches.  It  is  probable  that  the  truth  lies  somewhere 
between  the  two  estimates. 


DEW.  179 

of  heat  to  maintain  a  state  of  equilibrium,  tlie  surface  of  the  earth, 
being  the  warmer  body,  radiates  a  portion  of  its  superfluous  tem- 
perature into  the  surrounding  space  ;  and  thus  the  air  immediately 
in  contact  with  the  surface  becomes  cooled  below  the  point  of  sa- 
turation, and  gives  olT  a  portion  of  its  water  in  the  form  of  dew. 

We  formerly  stated  that  the  radiating  powers  of  bodies  differ 
exceedingly  according  to  their  composition,  the  nature  of  their  sur- 
face, their  colour,  &c.  These  differences,  of  course,  produce  cor- 
responding effects  on  the  deposition  of  dew  ;  and,  as  beautifully 
demonstrated  by  Dr.  Wells,  explain  its  greater  or  less  deposition 
under  certain  circumstances,  or  its  entire  absence  under  others. 
Thus,  what  formerly  appeared  so  extraordinary,  viz.  why  in  the 
self-same  state  of  the  atmosphere,  Sic.  one  portion  of  the  earth's 
surface,  or  one  portion  of  herbage,  should  be  covered  with  dew, 
while  another  in  the  immediate  neighbourhood  should  remain  dry, 
is  no  longer  a  mystery,  but  is  perfectly  explicable  on  the  suppo- 
sition of  their  different  radiating  powers. 

The  deposition  of  dew  is  always  most  abundant  during  calm 
and  cloudless  nights,  and  in  situations  freely  exposed  to  the  atmo- 
sphere. Whatever  interferes  in  any  way  with  the  process  of  ra- 
diation, as  might  be  expected,  has  a  great  effect  on  the  deposition 
of  dew.  Hence  the  radiation  of  heat,  and  consequently  the  deposi- 
tion of  dew,  is  not  only  obviated  by  the  slightest  covering  or  shel- 
ter, as  by  thin  matting,  or  even  muslin  ;  by  the  neighbourhood  of 
buildings,  and  innumerable  other  impediments,  near  the  earth's 
surface  ;  but  matters  interposed  at  a  great  distance  from  the  earth's 
surface  have  precisely  the  same  effect.  Thus  clouds  effectually 
prevent  the  radiation  of  heat  from  the  earth's  surface  ;  so  that 
cloudy  nights  are  always  warmer  than  those  which  are  clear,  and, 
in  consequence,  there  is  usually  on  such  nights  little  or  no  depo- 
sition of  dew. 

From  dew  there  is  an  insensible  transition  to  Hoar  Frosty  hoar 
frost  being  in  fact  only  frozen  dew,  and  indicative  of  greater  cold. 
We  observe,  therefore,  that  frosty  nights,  like  simply  dewy  nights, 
are  generally  still  and  clear. 

The  influence  of  radiation  in  producing  cold  at  the  earth's  sur- 
face would  scarcely  be  believed  by  inattentive  observers.  Often 
on  a  calm  night,  the  temperature  of  a  grass  plot  is  10°  or  15°  less 
than  that  of  the  air  a  few  feet  above  it.  Hence,  as  Mr.  Daniell 
has  remarked,  vegetables,  in  our  climate,  are  during  ten  months 
of  the  year  liable  to  be  exposed  at  night  to  a  freezing  temperature, 
and  even  in  July  and  August  to  a  temperature  only  two  or  three 
degrees  warmer.  Yet,  notwithstanding  these  vicissitudes,  in  the 
words  of  the  same  gentleman, — "  To  vegetables  growing  in  cli- 
mates for  which  they  are  originally  designed  by  nature,  there  can 
be  no  doubt  that  the  action  of  radiation  is  particularly  beneficial, 


180  METEOROLOGY. 

from  the  deposition  of  moisture  which  it  determines  upon  the  fo- 
liage ;  and  it  is  only  to  tender  plants,  artificially  trained  to  resist 
the  rigours  of  an  unnatural  situation,  tliat  this  extra  degree  of  cold 
proves  injurious."-^  It  may  be  observed  also,  that  trees  of  lofty 
growth  frequently  escape  being  injured  by  frost,  when  plants 
nearer  tlie  ground  are  quite  destroyed. 

Such  is  the  explanation  of  the  phenomena  of  dew  now  univer- 
sally admitted,  of  the  general  accuracy  of  which  there  cannot  be 
the  least  doubt.  But,  we  may  ask,  are  all  the  phenomena  of  dew 
strictly  referrible  to  radiation  ?  and  does  not  a  portion  of  the  water 
deposited  as  dew  arrive  at  the  earth's  surface  by  diffusion  from 
the  higher  and  colder  regions  of  the  atmosphere,  as  formerly  sug- 
gested ? 

Of  Mists  and  Fogs. — Mists  are  not  necessarily  connected  with 
the  deposition  of  dew,  because  during  the  deposition  of  dew  the 
atmosphere  often  continues  transparent,  even  to  the  earth's  sur- 
face. At  other  times,  however,  and  for  reasons  which,  in  the 
present  state  of  our  meteorological  knowledge,  cannot  be  satisfac- 
torily explained,  the  deposition  of  dew  is  accompanied  by  a  visi- 
ble vapour  or  mist,  more  or  less  dense,  and  extending  from  the 
surface  of  the  earth  to  a  greater  or  less  height  in  the  atmosphere. 
When  mists,  from  other  causes,  are  general,  and  extend  to  consi- 
derable heights  above  the  earth's  surface  they  acquire  the  name  of 
fogs.  The  optical  properties  and  the  buoyancy  in  the  atmosphere 
of  mists  and  fogs,  would  seem  to  mdicate  that  they  are  not  formed 
of  solid  particles,  but  of  minute  hollow  vesicles,  having  the  quality 
of  mutual  repulsion;  the  tendency  to  repel  each  other,  preventing 
the  coherence  of  the  vesicles  into  drops,  at  least  under  ordinary 
circumstances.  These  vesicles  have  been  occasionally  observed 
of  considerable  magnitude.  Thus  Saussure,  in  one  of  his  Alpine 
journeys,  saw  vesicles  float  slowly  before  him  having  greater  di- 
ameters than  peas,  and  whose  coating  seemed  inconceivably  thin. 
It  is  proper  to  mention,  however,  that  there  is  diversity  of  opinion 
respecting  the  actual  constitution  of  visible  vapour. 

That  the  cause  of  the  formation  of  mists  and  of  fogs  is,  to  a 
certain  extent,  similar  to  that  of  the  formation  of  dew,  appears  by 
their  prevalence  over  rivers  and  large  masses  of  water,  especially 
durin<r  the  autumnal  months.  The  radiation  of  heat  from  the 
land  and  from  the  water  is  at  tliese  seasons  very  different ;  the 
difference  being  greatest  when  the  temperature  of  the  water  ap- 
proaches 40°,  its  point  of  maximum  density.  The  water  is  then 
of  a  temperature  nearly  uniform,  both  by  day  and  by  night,  while 
the  temperature  of  the  land  is,  during  the  day,  much  higher  than 
40°  and  during  the  night,  often  much  under  that  temperature. 

•  Meteorological  Essays  and  Observations,  p.  511,  second  edition. 


MISTS  AND  FOGS.  131 

The  water  in  most  cases  occupying  the  lowest  situations  ;  when- 
ever, from  the  inequalities  of  the  surface  of  the  land,  or  from  any 
other  cause,  the  colder  air  produced  by  radiation  over  the  land,  is 
made  to  mix  itself  with  the  warmer  air  over  the  water,  the  mois- 
ture in  the  warmer  air  is  condensed  so  as  to  become  mist.  Hence 
the  formation  of  mist  differs  slightly  from  that  of  dew,  inasmuch 
as  there  is  occasionally  (not  always)  an  intermixture  of  air  of  dif- 
ferent temperatures.  The  reason  is  thus  evident  of  the  fogs  and 
mists  so  frequently  seen  over  rivers  and  in  valleys,  or  in  other 
situations  where  there  is  a  collection  of  water.  The  occurrence 
of  these  mists  is  usually  on  clear  and  cold  nights, — oftener  in 
autumn,  and  seldom  or  never  in  cloudy  weather  ;  the  state  of  the 
atmosphere  having  exactly  ihe  same  influence  on  them,  as  on  the 
deposition  of  dew.  'J'here  cannot  be  a  doubt  that  these  mists,  like 
clouds,  produce  a  great  eifect  in  impeding  radiation,  and  in  thus 
mitigating  the  intensity  of  cold.  Mists  are  therefore  of  much  im- 
portance in  the  economy  of  nature.  Plants  growing  in  low 
grounds  are  by  them  shielded  from  the  destroying  influence  of  the 
sudden  cold,  that  would  almost  certainly  be  produced,  not  only  by 
the  free  radiation  of  heat  in  such  situations,  but  by  the  descent  of 
cold  air  from  the  surrounding  high  grounds. 

The  fogs  that  hang  over  great  towns  admit  of  an  explanation 
similar  to  that  of  other  aqueous  fogs.  The  air  of  the  town  being 
warmer  than  that  of  the  surrounding  country,  and  being  at  the 
same  time  charged  with  moisture  nearly  to  the  point  of  satura- 
tion, is,  in  cold  weather,  suddenly  cooled,  either  by  the  radiation 
of  its  own  heat,  or  by  the  admixture  of  the  neighbouring  cold 
air  ;  while  the  superfluous  moisture  is  condensed  as  a  fog. 

The  fogs  of  high  latitudes,  more  especially  the  fogs  of  the 
Polar  seas,  are  in  the  same  manner  owino-  to  the  radiation  of 
heat.  The  cooling  of  the  warmer  air  over  the  immense  masses 
of  floating  ice,  gives  rise  to  an  unequal  distribution  of  temperature, 
and  thus  at  certain  seasons,  to  uninterrupted  fogs.  In  all  these  in- 
stances the  effect  of  fogs  is  probably  beneficial  in  alleviating  the 
severity  of  cold  by  checking  great  and  sudden  alternations  of 
temperature,  which  would  otherwise  interfere  much  with  the 
operations  of  organic  life. 

Fogs  have  been  sometimes  observed  of  a  strong  odour,  appa- 
rently the  result  of  an  admixture  of  foreign  bodies.  In  a  subse- 
quent paragraph  these  fogs  will  be  fully  considered. 

Of  Clouds. — From  mists  and  fogs  the  transition  to  clouds  is 
easy  and  natural ;  as  clouds,  in  reality,  are  nothing  more  or  less 
than  masses  of  visible  vapour,  precisely  similar  to  that  compos- 
ing fogs,  but  existing  at  a  distance  above  the  earth's  surface. 
Clouds  diflfer  principally  from  mists  and  fogs  in  their  mode  of 
formation.     Thus  mists,  like  dew,  as  we  have  seen,  are  the  re- 

16 


182  METEOROLOGY. 

suits  of  the  cooling  of  the  lower  strata  of  the  atmosphere  by  ra- 
diation. Fogs  are  so  far  the  result  of  radiation  that  they  usually 
arise  from  the  influence  that  air  cooled  by  radiation,  exerts  on 
warmer  air.  While  clouds  probably  depend  altogether  on  con- 
vection,  and  result  from  the  intermixture  of  strata  of  air  of  dif- 
ferent temperatures,  and  in  different  states  of  saturation,  in  the 
higher  regions  of  the  atmosphere. 

Such  is  the  general  opinion  of  the  formation  of  clouds  ;  but  it 
must  be  confessed  that  there  are  considerable  difficulties  about  the 
subject ;  and  that  the  mere  assumption  of  strata  of  diff'erent  tem- 
peratures, more  or  less  saturated  with  vapour,  and  having  the 
proper  motions  supposed  to  depend  upon  such  different  tempera- 
tures and  degrees  of  saturation,  seems  quite  inadequate  to  account 
for  all  the  phenomena  connected  with  the  formation  and  appear- 
ance of  clouds.  May  not  many  of  the  phenomena  of  clouds  de- 
pend upon  the  diffusion  of  vapour  from  cold  and  distant  regions  ? 
May  not  other  phenomena  result  from  the  more  or  less  sudden 
decomposition  (by  electricity  ?)  of  the  deutoxide  of  hydrogen 
which  we  conceive  to  exist  in  the  atmosphere  ? 

From  the  principles  formerly  stated  when  we  described  the 
phenomena  and  properties  of  a  mixed  atmosphere  of  air  and  va- 
pour, it  appears  that  clouds  in  general  must  be  formed  at  that 
elevation  in  the  atmosphere  in  which  the  mean  temperature  of 
the  air  becomes  equal  to,  or  falls  below  the  point  of  saturation  of 
such  air.  This  elevation  which  may  be  said  to  constitute  the 
region  of  clouds,  must  of  course  be  highest  under  the  Equator — 
an  inference  supported  by  fact ;  for  it  has  been  observed  that 
within  the  tropics,  the  clouds  are  most  frequently  higher  than  in 
the  temperate  zones  ;  and  in  the  temperate  zones  the  clouds  ap- 
pear to  be  higher  in  summer  than  they  are  in  winter.  In  the 
temperate  zones  Gay  Lussac  thinks  that  clouds,  in  general,  are 
upheld  at  an  average  distance  from  the  earth's  surface  of  between 
1500  and  2000  yards.  Occasionally,  however,  clouds  have  a 
much  greater  altitude  ;  and  the  Cirnis,  a  form  of  cloud  to  be 
presently  described,  has  been  seen  far  above  the  greatest  elevation 
hitherto  attained  by  man. 

In  some  parts  of  the  world  clouds  are  rarely  seen,  M'hile  in 
other  parts  the  sky  is  seldom  cloudless.  Such  extremes  are 
usually  confined  to  extreme  climates,  or  depend  upon  local  causes. 
In  the  temperate  zones,  from  the  irregularity  of  tlie  atmospheric 
currents,  and  from  the  other  innumerable  circumstances  calculated 
to  disturl)  the  equilibrium  of  the  atmosphere,  the  general  character 
of  clouds  varies  much  even  under  the  same  parallel  of  latitude. 
Hence  all  the  infinite  variety  of  sunshine,  of  cloud,  and  of  shower, 
which  more  especially  distinguish  the  temperate  zones,  and  our 


CLOUDS.  183 

own  variable  sky  in  particular;  where  ihey  exert  such  constant 
and  commanding  influence  upon  our  comfort  and  well-being,  as  to 
become  almost  interwoven  with  our  very  existence. 

Though  clouds  are  of  such  endless  diversity  o^  figure  and  ap- 
pearance, they  have  been  classed  by  Howard  under  three  primary 
forms,  and  four  modifications.     The  three  primary  forms  are  : 

The  Cirrus,  composed  of  fibrous-like  stripes,  parallel,  flexuous, 
or  diverging,  and  extensible  in  all  directions. 

The  Cumulus,  heaped  together  in  convex,  or  in  conical  masses, 
and  increasing  upwards  from  a  horizontal  base. 

The  Stratus,  spreading  horizontally  in  a  continuous  layer,  and 
increasing  from  below. 

The  first  of  these  forms,  the  cirrus,  is  confined  chiefly  to  the 
higher  regions  of  the  atmosphere.  The  second  form,  the  cu- 
mulus occupies  a  lower  but  still  an  elevated  station  ;  while  the 
third  form,  the  stratus,  usually  rests  on  the  surface  of  the  earth, 
constituting  the  mist  already  described  in  this  chapter. 

Of  the  four  modified  forms  of  clouds,  two  are  intermediate,  and 
two  are  composite. 

The  first  of  the  intermediate  forms  is  the  Cirro-CumuIus, 
consisting  of  small  roundish,  and  well-defined  masses  in  close 
horizontal  arrangement. 

The  masses  that  compose  the  second  intermediate  form  of 
clouds,  the  Cirro- Stratus,  are  likewise  small  and  rounded,  and 
are  attenuated  towards  a  part  or  towards  the  whole  of  their  cir- 
cumference. They  are  sometimes  separate  ;  when  in  groups, 
their  arrangement  is  either  horizontal,  or  slightly  inclined,  and 
the  masses  are  either  bent  downwards,  or  are  undulated. 

Of  the  two  composite  forms  of  clouds,  the  first  is  the  Cumulo- 
Stratus,  made  up  of  the  Cirro-Stratus  blended  with  the  Cumulus  ; 
the  Cirro-Stratus  being  either  intermingled  with  the  larger  masses 
of  the  Cumulus,  or  widely  enlarging  the  cumulous  base. 

The  second  composite  form,  and  the  last  of  the  four  modifica- 
tions, of  clouds,  is  the  Cumulo-Cirro- Stratus,  or  JVhnbus,  the 
raiii- cloud ;  being  that  cloud  or  system  of  clouds  from  which 
rain  is  falling.  The  nimbus  is  a  horizontal  layer  of  aqueous  va- 
pour, over  which,  clouds  of  the  cirrous  form  are  spread,  while 
other  clouds  of  the  cumulous  form  enter  it  laterally  and  from  be- 
neath. 

A  little  attention  will  enable  any  one  to  discriminate  these  va- 
rieties of  clouds,  at  least  when  their  forms  are  well  defined.  Yet, 
it  must  be  acknowledged  that  clouds  often  assume  forms  to  which 
it  is  difficult  to  give  a  name. 

With  respect  to  the  motion  of  clouds,  it  may  be  remarked  that 
there  is  not  perhaps  a  more  frequent  subject  of  optical  delusion, 
nor  anything  regarding  which,  we  are  more  liable  to  be  mistaken, 


184  METEOROLOGY. 

Into  such  inquiry  it  would  be  quite  inconsistent  with  the  design 
of  this  treatise  were  we  to  enter  minutely ;  but  we  offer  the  fol- 
lowing brief  illustration.  Let  us  suppose  a  cloud  moving  from 
the  distant  horizon  towards  the  place  where  we  stand.  Let  us 
also  suppose  that  the  cloud  during  its  motion  retains  the  same  size 
and  figure,  and  that  it  proceeds  along  its  course  in  a  uniform 
horizontal  line.  A  cloud  so  moving,  when  first  seen,  will  appear 
to  be  in  contact  with  the  distant  horizon  ;  and  will  thus  necessa- 
rily, from  its  remote  position  appear  to  be  much  smaller  than  in 
reality  it  is.  During  its  advance  towards  us,  the  cloud  will  seem 
to  rise  into  the  sky,  and  to  become  gradually  larger,  till  it  is  al- 
most directly  overhead.  Continuing  its  progress  it  will  then 
seem  again  to  descend  from  the  zenith,  and  to  lessen  in  size  as 
gradually  as  it  had  before  increased,  till  at  last  it  vanishes  in  the 
distance,  opposite  to  where  it  commenced  its  movement.  Thus 
the  same  cloud,  without  deviating  from  its  motion  in  a  straight 
line,  and  retaining  throughout  the  same  size  and  figure,  will,  by 
optical  delusion,  seem  continually  to  vary  in  magnitude.  The 
line  of  its  motion  also,  instead  of  being  straight,  will  appear  to  be 
a  curve  having  its  vertex  directly  above  us,  and  its  extremes 
boundless  in  opposite  points  of  the  horizon.  We  have  given  the 
most  simple  case  that  can  be  supposed.  But  clouds,  as  they  ex- 
ist in  nature  are  unceasingly  varying  in  shape,  in  magnitude,  in 
direction,  and  in  velocity;  so  that  to  form  a  just  estimate  of  their 
figure  and  direction,  or  to  unravel  their  motions,  becomes  abso- 
lutely impossible. 

After  what  has  been  stated,  it  will  be  superfluous  to  dwell  upon 
the  uses  of  clouds  in  the  economy  of  nature  ;  we  shall  therefore 
briefly  remind  the  reader  of  a  few  only  of  the  most  obvious  be- 
nefits derived  from  clouds.     The  first  of  these  that  claims  our  at- 
tention is,  that  upon  the  large  scale  at  least,  clouds  constitute  a 
sort  of  intermediate  state  of  existence  between  vapour  and  water, 
by  which  sudden  depositions  of  water  and  their  consequences  are 
entirely  prevented.     If  all  the  water  separated  from  the  atmo- 
sphere fell  at  once  to  tlie  earth,  in  the  slate  of  water,  we  should 
be   constanUy  liable   to  deluges  and  other  inconveniences,   the 
whole  of  which  are  obviated  by  the  present  beautiful  arrangement. 
Again  clouds  are  one  great  means  by  which  water  is  transported 
from  seas  and  oceans  to  be  deposited  far  inland,  where  water 
otherwise  would  never  reach.     Clouds  also  greatly  mitigate  the 
extremes  of  temperature.     By  day  they  shield  vegetation  from 
the  scorching  influence  of  the  solar  heat,  and   produce  all  the 
agi'ecable  vicissitudes  of  shade  and  sunshine  :  by  night,  the  earth, 
wrapt  in  its  mantle  of  clouds,  is    enabled  to   retain    that   heat 
which  would  otherwise  radiate  into  space,  and  is  thus  protected 
from  the  opposite  influence  of  the  nocturnal  cold.     These  bene- 


SNOW.  185 

fits  arising  from  clouds  are  most  felt  in  countries  without  the  Tro- 
pics, which  are  most  liable  to  extremes  of  temperature,  Indeed, 
clouds  constitute  one  great  means  by  which,  in  temperate  climates, 
the  extremes  of  heat  and  cold  are  regulated.  Lastly,  whether  we 
contemplate  them  with  respect  to  their  form,  their  colour,  their 
numerous  modifications,  or,  more  than  all,  their  incessant  state 
of  change,  clouds  prove  a  source  of  never-failing  interest,  and  may 
be  classed  among  the  most  beautiful  objects  in  nature. 

Having  finished  the  consideration  of  the  various  states  of  visi- 
ble vapour,  we  are  now  to  examine  the  phenomena  of  the  preci- 
pitation of  water  from  the  atmosphere  in  the  form  of  Snow,  Sleet, 
Rain^  and  Hail.     We  shall  first  speak. 

Of  Snow. — We  commence  with  snow  because  it  offers  the 
most  simple  case  of  the  precipitation  of  water  from  the  atmo- 
sphere ;  snow  being  nothing  more  than  the  frozen  visible  vapour 
composing  clouds.  Hence  a  flake  of  snow  examined  with  a 
high  magnifier  exhibits  a  beautiful  display  of  minute  crystals, 
often  possessing  the  greatest  variety  of  form. 

W^hen  the  temperature  of  the  atmosphere,  down  to  the  enrth's 
surface,  is  constantly  below  the  freezing  point,  it  is  obvious  that 
any  moisture  separated  from  the  atmosphere  must  assume  the 
solid  form.  If  the  quantity  separated  be  small,  the  frozen  parti- 
cles of  water  remaining  detached,  float  in  the  atmosphere  in  the 
form  of  crystallized  spiculae,  and  thus  give  origin  to  what  is  called 
ihe  frost-smoke,  a  phenomena  not  unfrequently  witnessed  in  polar 
latitudes.  Even  in  temperate  climates,  the  same  thing  has  been 
supposed  occasionally  to  take  place  in  the  higher  regions  of  the 
atmosphere,  and  thus  to  produce  certain  optical  phenomena  to 
which  we  shall  hereafter  refer. 

The  above  are  comparatively  rare  phenomena.  Most  generally 
the  quantity  of  water  separated  is  so  large  that  the  crystallized 
particles  are  agglutinated  together  into  masses  or  flakes,  and  thus 
fall  to  the  earth  in  the  form  of  snow.  When  the  quantity  depo- 
sited is  very  great,  as  is  often  the  case,  there  can  be  no  doubt  that 
the  causes  operating  to  produce  such  large  deposition,  are  pre- 
cisely similar  to  those  which  produce  rain  in  warmer  climates, 
and  which  will  be  considered  in  a  subsequent  paragraph. 

Such,  in  few  words,  are  the  principles  upon  which  snow  is 
formed,  and  from  these  the  reason  is  at  once  apparent,  why  during 
the  winter  in  temperate  climates,  and  throughout  the  whole  year 
in  the  polar  climates,  most  of  the  water  that  falls  to  the  earth  as=. 
sumes  the  form  of  snow. 

We  formerly  mentioned  how  nwich  we  owe  to  the  lohiteness 
of  snow  ;  and  we  may  now  remark  that  we  owe  still  more  to  its 
low  co^nducting  properties,  and  to  its  lightness.  Thus  by  its 
low  conducting  properties  snow  shields  vegetation  from  the  rigo=^ 

16* 


:^ 


186  METEOROLOGY. 

roiis  cold  of  the  higher  latitudes,  where  everything  herbaceous  would 
be  destroyed  during  the  winter,  were  it  not  for  the  protecting  in- 
fluence of  snow.  Again  if  the  water  which  now  descends  to  the 
earth  as  snow,  were  to  be  precipitated  in  the  form  of  solid  masses 
of  ice,  vegetation  would  be  destroyed,  and  the  whole  of  the  colder 
parts  of  the  earth  would  be  uninhabitable  ! 

It  has  been  remarked,  in  temperate  climates  more  especially, 
that  the  air  is  usually  warmer  during  a  fall  of  snow,  than  before 
or  after.  This  increase  of  temperature  probably  arises  from  the 
extrication  of  heat  in  the  sensible  form  durino;  the  transition  of  the 
vapour  from  a  fluid  to  a  solid  state.  Snow^-water  has  also  been 
said  to  contain  much  oxygen,  and  thus  to  be  particularly  favoura- 
ble to  vegetation. 

Sleet  is  snow  in  a  half  melted  condition,  and  constitutes  the 
intermediate  state  between  snow  and  rain,  to  be  next  considered. 

Of  Rain. — When  the  temperature  of  the  air  is  above  32°,  the 
freezing  point  of  water,  the  water  separated  from  the  air  falls  to 
the  earth  in  the  state  of  rain.  Such  is  a  general  expression  of 
the  fact ;  but  after  all  the  attention  that  has  been  bestowed  on  the 
phenomena  of  rain,  many  difficulties  attend  the  investigation,  that 
have  not  yet  been  surmounted. 

It  cannot  be  doubted  that  rain  is  in  some  way  connected  with 
change  of  temperature ;  the  perplexity  attending  the  subject, 
arises,  pardy  from  the  impossibility  in  many  instances  of  account- 
ing for  the  supposed  change  of  temperature  ;  but  much  more  from 
the  difficulty  of  understanding  how  this  change  of  temperature 
operates.  According  to  the  usual  opinion,  the  precipitation  of 
water  from  the  atmosphere  is  the  effect  of  the  mingling  together 
of  currents  of  warm  and  of  cold  air,  which  are  supposed  to  ope- 
rate on  each  other  in  the  following  manner. 

From  the  law  of  the  tension  of  vapour,  already  described,  it 
follows,  that  when  two  currents  of  air  having  dilferent  tempera- 
tures, but  both  alike  saturated  with  vapour,  are  mixed  togetlier ; 
though  the  resulting  temperature  of  the  mixture  will  be  the  mean 
of  the  two,  the  resuhing  tension  of  the  vapour  will  not  be  likewise 
the  mean.  The  resulting  tension  of  the  vapour  will  always  ex- 
ceed the  tension  belonging  to  the  resulting  mean  temperature  ; 
consequently  there  will  be  an  excess  of  vapour  which  will  be 
precipitated  in  the  form  of  water.  Thus  let  us  suppose  two  cur- 
rents of  air,  both  saturated  with  vapour,  the  one  having  a  tempe- 
rature of  40°,  and  the  other  a  temperature  of  60°  and  that  these 
two  currents  of  air  are  mingled  together ; 

Inches  of  Mercury. 
The  tension  or  ekistic  force  of  vapour  at  40°  is  eqnul  to     -     .263 
of  vapour  at  60°  is     -     -     -     -     .524 


RAIN.  187 

Whence  it  appears  that  the  mean  temperature  of  the  two  volumes 
of  air  is  50°,  and  the  mean  of  the  elasticities  of  their  vapour  .393 
inches.  But  the  actual  tension  or  elastic  force  of  vapour  at  50° 
is  not  .393  inches,  but  only  .375  inches ;  after  the  intermixture, 
therefore,  of  the  two  currents,  a  quantity  of  vapour  will  remain, 
proportionate  to  the  tension  of  0.18  inches  ;  and  as  this  superflu- 
ity of  vapour  cannot  be  held  in  solution  by  air  of  the  mean  tem- 
perature of  50°,  it  will  be  separated  in  the  form  of  clouds,  or  of 
rain,  according  to  circumstances. 

Such,  in  few  words,  are  the  opinions  respecting  rain  first  ad- 
vanced by  Dr.  Hutton  ;  and  notwithstanding  some  difficulties 
about  these  opinions,  there  can  be  little  doubt  of  their  general 
accuracy.  The  subject  of  condensation,  in  general,  may  perhaps 
receive  some  additional  elucidation  from  the  principles  regulating 
a  mixed  atmosphere  of  vapour  and  air  formerly  described  ;  and 
which  may  be  thus  applied.  When  two  currents  of  atmospheric 
air  of  diff'erent  temperatures,  and  each  charged  with  vapour  up  to 
the  point  of  saturation,  are  brought  into  contact ;  they  will  begin 
to  intermingle  in  virtue  of  the  proper  motions  of  the  air  and  va- 
pour, and  the  immediate  result  will  be  the  formation  of  visible 
vapoKT,  that  is  to  say,  of  a  cloud.  If  the  currents  are  continuous 
and  uniform,  the  clouds  soon  spread  in  all  directions,  so  as  to  oc- 
cupy the  whole  horizon  ;  while  ihe  additional  moisture  incessantly 
brought  by  the  warmer  current,  or  the  occasional  difl'usion  of 
vapour  from  a  distant  and  colder  region,  keeps  up  a  constant 
supply  for  condensation,  and  produces  a  great  and  continued  de- 
position of  moisture  in  the  form  of  rain.  By  degrees  the  currents 
completely  intermingle,  and  acquire  a  uniform  temperature  ;  con- 
densation then  ceases,  the  clouds  are  redissolved,  and  the  whole 
face  of  nature,  after  being  cooled  and  refreshed  by  the  necessary 
rain,  is  again  enlivened  by  the  sunshine,  thus  rendered  slill  more 
agreeable  by  its  contrast  with  the  previous  gloom. 

In  this  manner  the  principles  formerly  detailed  may  be  applied 
to  the  explanation  of  the  phenomena  of  rain  ;  and  as  far  as  the 
explanation  goes  it  is  perhaps  quite  satisfactory.  It  must,  how- 
ever, be  allowed,  as  we  have  before  stated,  that  the  utmost  infor- 
mation which  we  can  at  present  bring  to  bear  upon  the  subject  of 
the  general  condensation  of  moisture  from  the  atmosphere,  and  of 
rain  in  particular,  leaves  it  involved  in  considerable  obscurity. 

The  following  additional  particulars  regarding  the  ej/'ects  of  dif- 
ferent localities,  and  of  different  circinnslances  in  the  same  lo- 
cality which  appear  to  influence  the  fall  of  rain,  may  interest  the 
general  reader. 

It  has  been  remarked  that  in  the  greater  nnmber  of  instances 
more  rain  falls  in  tlie  neighbourhood  of  the  sea  than  in  the  sea; 
a  fact  easily  understood  from  the  principles  that  have  been  stated. 


188  METEOROLOGY. 

Among  mountains  also  more  rain  falls  than  on  plains;  the  excess 
is  indeed  striking.  Thus  in  our  own  country,  at  Kendal  and  at 
Keswick,  both  inclosed  by  mountains,  the  annual  fall  of  rain 
amounts  to  67i  and  54  inches  respectively,  while  in  many  inland 
places  the  quantity  of  rain  that  falls  in  the  course  of  a  year  hardly 
exceeds  25  inches.  So  at  Paris,  the  annual  fall  of  rain  is  only 
about  20  inches,  but  at  Geneva  42|  inches  ;  and  on  the  Great  St. 
Bernard,  the  highest  meteorological  station  in  Europe,  upwards 
of  63  inches  of  rain  fall  during  the  twelve  months. 

Although  more  rain  falls  in  mountainous  districts  than  in  plains, 
it  has  been  completely  established,  that  more  rain  falls  at  the  foot 
of  a  mountain,  than  on  its  top.  In  general,  too,  a  larger  propor- 
tion of  rain  is  separated  from  the  air,  near  the  eartNs  surface, 
than  at  any  height  above  it ;  a  discrepancy  of  which  the  present 
extent  of  our  knowledge  does  not  enable  us  to  give  a  satisfactory 
explanation. 

In  most  Tropical  countries  rain  falls  only  at  particular  seasons 
of  the  year,  there  being  scarcely  any  rain  during  the  other  seasons. 
Thus,  at  Bombay,  the  rainy  months  are  June.  July,  August, 
September,  and  October,  while  the  other  months  are  almost  with- 
out rain  ;  but  on  the  opposite  side  of  India,  along  the  Coromandel 
coast,  the  time  of  the  occurrence  of  the  rainy  season  is  reversed; 
a  fact  strikingly  illustrative  of  the  effect  of  the  intervention  of  the 
high  table  land  that  separates  the  two  coasts,  and  which  probably, 
by  influencing  the  atmospheric  currents,  give  rise  to  this  singular 
alternation  of  weather. 

In  temperate  climates,  though  the  total  quantity  of  rain  that 
falls  be  much  less  than  within  the  Tropics,  there  is  no  protracted 
dry  season  ;  and  the  rainy  days  in  the  year  are  more  numerous 
the  nearer  we  go  to  the  Poles.  Still  in  general,  more  rain  seems 
to  fall  in  temperate  climates  during  the  last  six,  than  during  the 
first  six  months  of  tiie  year. 

Among  tiie  circumstances  which  influence  the  quantity  of  rain 
in  the  same  locality,  the  most  remarkable  are  diminution  of 
temperature^  and  the  unusual  prevalence  of  certain  ivinds. 

With  respect  to  diminution  of  temperature  it  has  been  observed 
that  almost  all  wet  seasons,  or  at  least  wet  summers,  in  temperate 
climates,  are  unusually  cold.  Now  from  the  principles  formerly 
advanced  it  will  be  easily  understood,  how  a  depression  of  the 
temperature  below  the  general  standard  in  any  locality,  may  give 
rise  to  a  greater  precipitation  of  moisture  in  that  locality.  The 
locality  that  has  become  colder  than  those  around  it,  acts  as  a 
refrigeratory,  and  not  only  condenses  and  thus  deprives  of  their 
elastic  force,  all  the  vapours  that  are  in  contact  with  it;  but  the 
neighbouring  vapours  rush  towards  the  colder  locality  as  towards 
a  vacuum,    either  in  the  form  of  visible   vapour   or  clouds,  in 


HAIL.  189 

which  case  they  are  carried  by  the  winds  ;  or  as  invisible  vapour, 
in  which  form,  their  movement  may  be  determined  by  diffusion. 

The  effect  of  the  tmusual prevalence  of  certain  winds  in  pro- 
ducing an  increase  of  rain,  or  tlie  reverse,  is  well  known,  and  is 
quite  intelligible  on  the  principles  we  have  explained.  Thus  in 
tropical  climates,  during  the  steady  prevalence  of  the  trade  winds, 
the  currents  intermingle  but  little,  the  atmosphere  is  perfectly 
cloudless,  and  no  condensation  takes  place.  But  when  these 
great  currents,  following  the  course  of  the  sun,  begin  at  certain 
seasons  of  the  year  to  shift  their  direction ;  their  uniform  course 
suffers  derangement,  they  become  intermixed,  and  condensations 
of  moisture  commensurate  with  the  high  temperature,  are  pro- 
duced to  an  extent  quite  unknown  in  temperate  climates.  These 
condensations  form  the  violent  periodical  rains  of  hot  climates. 
So  also  in  temperate  climates,  as  for  instance  in  our  own  country, 
winds  coming  from  the  south  and  from  the  west,  are  from  a 
warmer  climate,  and  hold  much  vapour  in  solution ;  while  winds 
from  the  opposite  points  are  colder,  and  therefore  relatively  drier. 
Hence  winds  from  the  south  and  from  the  west,  are  more  fre- 
quently accompanied  by  rain,  than  winds  from  the  north  and  from 
the  east :  though  as  we  might  expect,  the  precipitation  of  rain  is 
most  decided  during  the  conflicts  between  these  opposite  currents, 
which  sometimes  extend  over  a  large  tract  of  country.  The  long 
prevalence  of  certain  winds  may  thus  cause  the  seasons  to  be  wet 
in  one  part  of  the  world,  and  dry  in  another;  the  water  being  as 
it  were,  distilled  off  from  the  one,  in  order  that  it  may  be  precipi- 
tated on  the  other.  Yet  the  whole  amount  of  the  rain  in  the  two 
countries  may  perhaps  differ  very  little  from  the  usual  average, 
while  the  two  countries  have  the  benefit  of  variety  in  the  general 
amount  of  their  rain ;  which  variety  may  be  salutary  at  particular 
periods,  and  may  even  be  necessary  to  their  well-being. 

Before  we  end  the  examination  of  the  phenomena  of  rain,  it  may 
be  proper  to  advert  to  the  generally  admitted  influence  of  the  Moon 
on  the  weather,  and  especially  on  the  fall  of  rain.  This  influence, 
however,  can  hardly  in  the  present  state  of  our  knowledge  be 
brought  to  elucidate  the  phenomena  of  rain  ;  so  great  are  the  dis- 
turbing effects  of  local  and  other  peculiarities. 

Of  Hail. — The  last  form  in  which  we  have  to  consider  the  pre- 
cipitation of  water  from  the  atmosphere,  is  hail.  Hail  may  be  re- 
garded as  consisting  of  drops  of  rain  more  or  less  suddenly  frozen 
by  exposure  to  a  temperature  below  32°.  If  the  degree  of  cold 
has  been  very  sudden  and  intense,  which  is  often  the  case,  the 
icy  nucleus,  from  its  being  of  a  temperature  far  below  the  freezing 
point,  acquires  magnitude  as  it  descends,  by  condensing  on  its 
surface  the  vapour  of  the  lower  regions  of  the  atmosphere.  Hence, 
even  under  ordinary  circumstances,  hail  stones  often  become  of 


190  METEOROLOGY. 

considerable  size,  are  nearly  always  more  or  less  rounded,  and 
when  broken  are  seen  to  be  composed  of  concentric  layers. 

From  what  has  been  stated  it  will  be  readily  inferred  that  hail 
is  not  a  product  of  extreme  climates  ;  indeed  hail  may  be  said  to 
be  peculiar  to  temperate  climates,  as  it  rarely  ever  occurs  beyond 
the  latitude  of  60°.  Hail  is  most  frequent  in  spring  and  in  sum- 
mer, when  it  is  often  accompanied  by  thunder.  It  seldom  hails 
in  winter,  and  hail  during  the  night  is  very  uncommon.  In  tro- 
pical countries  there  is  little  hail  in  any  place  that  is  not  more 
than  2000  feet  above  the  level  of  the  sea:  in  temperate  climates, 
on  the  contrary,  mountain  tops  are  almost  free  from  hail.  Certain 
countries,  especially  some  parts  of  France,  are  very  liable  to  hail 
storms  ;  and  such  is  at  times  the  fury  of  these  storms  that  they 
lay  waste  whole  districts.  There  are  on  record  many  instances 
of  these  calamitous  visitations,  which  are  usually  accompanied 
by  whirlwinds  and  by  the  most  appalling  electrical  phenomena. 
During  storms  of  such  degree  of  severity,  hail  stones  have  some- 
times fallen  of  enormous  magnitude,  and  often  of  an  irregular 
shape,  as  if  they  were  the  fragments  of  a  thick  sheet  of  ice  suddenly 
broken  :  a  supposition  which  alone  will  explain  the  formation  of 
angular  masses,  many  inches  in  size,  and  many  pounds  in  weight. 
The  production  in  the  middle  of  summer  of  the  intense  cold  that 
is  thus  indicated  is  a  puzzle  which  philosophers  have  been  unable 
to  solve. 

Of  the  Distribution  of  Heat  and  Light  in  their  latent  and  de- 
composed Forms  through  the  Vapour  of  the  Atmosphere  ;  and 
of  the  Effects  of  that  Distribution. — The  general  distribution  of 
heat  and  light  in  their  latent  forms  through  the  vapour  of  the  at- 
mosphere, seems  to  follow  the  same  laws  as  the  distribution  of 
sensible  heat  formerly  explained.  That  is  to  say,  the  distribution 
of  these  forms  of  heat  and  light  decreases  from  the  Equator  toward 
the  Poles.  The  most  remarkable  effects  of  the  distribution  of  la- 
tent heat  have  already  been  incidentally  mentioned,  and  need  not 
be  here  repeated.  We  shall  therefore  proceed  to  consider  the  par- 
ticular distribution  of  the  decomposed  forms  of  heat  and  light  in 
the  vapour  of  the  atmosphere,  and  the  efiects  of  this  distribution. 

Of  the  Relations  of  Electricity  to  the  Vapour  of  the  Atmo- 
sphere.— Atmospheric  air,  when  perfectly  dry  and  pure,  is  one 
of  the  most  complete  non-conductors  of  electricity  that  are  known. 
Whether  water  in  the  state  of  vapour  possesses  similar  non-con- 
ducting properties  does  not  appear  to  be  satisfactorily  established. 
But  the  non-conducting  powers  of  aqueous  vapour  must  be  very 
considerable,  otherwise,  since  the  atmosphere  is  never  entirely 
free  from  vapour,  electrical  insulation  could  not  takd  place.  On 
the  other  hand,  the  moment  that  vapour  assumes  the  form  of  water, 
it  acquires  the  property  of  being  a  conductor  of  electricity.  Hence 


RELATION  OF  ELECTRICITY  TO  VAPOUR.  191 

a  mass  of  visible  vapour  or  cloud,  when  floating  in  a  mixed  atmo- 
sphere of  air  and  vapour,  is  perfectly  insulated,  and  is  thus  capa- 
ble of  electrical  accumulation.  Now  the  phenomena  arising  from 
the  equalization  of  such  derangements  of  electrical  distribution, 
are  lightning  and  thunder.  Lightning  and  thunder  therefore  are 
nothing,  either  more  or  less,  than  the  phenomena  of  electricity  on 
a  large  scale ;  that  is  to  say,  a  cloud  and  the  earth,  or  two  clouds, 
become  surcharged  with  the  two  opposite  forms  of  electricity,  and 
thus  represent  the  interior  and  the  exterior  coatings  of  an  electrical 
jar  similarly  surcharged  ;  the  intervening  and  non-conducting  air 
are  represented  by  the  interposed  and  non-conducting  glass  ; 
while  the  lightning  and  the  thunder  are  the  spark  and  the  explo- 
sion caused  by  the  union  of  the  two  electricities.  If  the  reader 
bear  in  mind  this  analogy,  it  will  enable  him  to  understand  the 
whole  electrical  phenomena  of  the  atmosphere. 

The  distribution  of  electricity,  like  that  of  heat  and  light,  de- 
creases from  the  Equator  toward  the  Poles.  Thus,  in  intertropi- 
cal countries  alone,  are  the  effects  of  this  energetic  agent  displayed 
in  all  their  power ;  there,  thunder  storms  are  quite  terrific,  and  far 
surpass  anything  of  which  those,  who  have  not  witnessed  them, 
can  form  a  conception.  In  temperate  climates  the  effects  of  at^ 
mospheric  electricity  are  usually  most  severe  in  the  summer;  and 
their  severity  is  greater  in  mountainous  districts  than  in  plains. 
Yet,  even  under  these  circumstances,  they  are  much  subdued,  as 
compared  "with  what  takes  place  between  the  Tropics  ;  while  in 
the  Polar  regions  electrical  phenomena  are  still  less  striking. 

Notwithstanding,  however,  that  the  general  distribution  of  elec- 
tricity in  the  atmosphere,  evidently  follows  the  general  distribu- 
tion of  sensible  heat,  it  is  a  remarkable  fact,  that  whenever  elec- 
trical phenomena  are  more  than  ordinarily  vehement,  they  are  ac- 
companied by  some  unusual  appearance  of  cold.  Thus  the  alarm- 
ing descents  of  hail  formerly  noticed,  which  occur  most  generally 
in  temperate  climates,  have,  in  nearly  every  instance,  been  attend- 
ants of  violent  thunder  storms.  Snow  also  is  almost  always  highly 
electric.  These,  and  manv  other  circumstances  connected  with 
the  great  and  sudden  production  of  cold  in  the  higher  regions  of 
the  atmosphere,  during  the  display  of  electrical  agency,  cannot, 
in  the  present  state  of  our  knowledge,  be  explained.  For  example, 
whence,  in  the  middle  of  summer,  arises  that  instantaneous  deve- 
lopement  of  extreme  cold,  which  occasionally  produces  the  terrific 
hail  storms  above  alluded  to  ?  At  present  the  answer  does  not  ap- 
pear. Whether  the  principles  advanced  in  the  present  volume 
be  capable  of  solving  the  difficulty,  time  must  determine. 

With  respect  to  the  sources  of  the  electricity  of  the  atmosphere 
there  have  been  many  opinions.  It  seems  now  to  be  admitted 
that  electrical  excitement  does  not  arise  from  the  mere  evapora- 


192  METEOROLOGY. 

tion  and  condensation  of  water  ;  but  that  in  order  to  produce  such 
excitement,  there  must  always  be  some  chemical  combination  or 
separation.*  Thus  electrical  excitement  is  the  result  of  the  che- 
mical changes  which  often  accompany  the  evaporation  of  water. 
During  combustion  also  there  is  an  ample  evolution  of  electricity  ; 
the  burning  body  giving  out  negative,  the  oxygen  positive  electri- 
city. In  like  manner,  the  carbonic  acid  sent  forth  during  vegeta- 
tion is  charged  with  negative  electricity,  and  at  the  same  time  the 
oxygen,  as  is  most  likely,  is  charged  with  positive  electricity. 
Derivation  from  these  sources  has  been  deemed  quite  sufficient  to 
explain  the  very  large  quantities  of  electricity  that  are  so  often  ac- 
cumulated in  the  clouds.  It  is  however  probable  that  there  are 
yet  other  causes,  or  at  least  one  other  cause,  on  which,  in  nume- 
rous instances,  this  accumulation  may  still  more  immediately  de- 
pend. AVe  allude  to  the  combination  of  oxygen  with  the  vapour 
of  the  atmosphere  formerly  mentioned.  For  reasons  which  we 
cannot  here  detail,  our  opinion  is,  that  this  combination  of  aque- 
ous vapour  with  oxygen,  more  than  any  other  cause  whatever,  is 
in  some  way  concerned  with  the  piienomena  of  atmospheric  elec- 
tricity. 

The  Jlurora  horeaUs  is  a  phenomenon  supposed  to  have  some 
connection  with  electricity,  though  its  precise  nature  is  involved 
in  considerable  obscurity.  The  phenomenon  evidently  indicates 
currents  of  some  kind  ;  and  if  the  light  be  electrical,  we  can  only 
suppose  such  electrical  currents  to  take  place  in  an  imperfectly 
conducting  medium.  That  is  to  say,  if  the  phenomenon,  as  some 
contend,  exist  in  the  lower  regions  of  the  atmosphere,  luminous 
electrical  currents  can  be  produced  only  by  water  in  the  liquid 
state  ;  if  the  phenomenon  exist  in  the  higher  regions  of  the  atmo- 
sphere, as  at  present  is  supposed,  such  currents  may  depend  upon 
the  extreme  tenuity  of  the  atmosphere  in  these  higher  regions. 
Our  own  opinion  is,  that  at  different  times,  the  aurora  borealis 
exists  at  different  heights  in  the  atmosphere,  and  consequendy 
may  depend  upon  both  these  causes.  Has  the  diffusion  of  vapour 
from  the  Polar  towards  the  Equatorial  regions  of  the  globe  any 
connexion  with  the  phenomenon  ? 

The  phenomenon  depending  upon  the  decomposition,  refrac- 
tion,  and  rejlection  of  light  by  the  vapour  of  the  'atmosphere 
are  not  less  striking  and  important  than  tliose  produced  by  electri- 
city. To  such  effects  upon  light  by  the  atmospheric  vapour  we 
owe  not  only  the  cacrulean  tint  of  the  sky,  and  all  the  splendid 
colouring  of  the  clouds,  but  tlie  beneficial  morning  and  even- 
ing twilight,  nay  even  the  light  of  day  itself.     "  Were  it  not," 

•  Pouillct,  Elemensde  Physique  experimentale  etde  Moteorolog-ie,  torn, 
ii.  p.  823. 


MIRAGE.       FATA  MORGANA.       HALOS,  ETC.  193 

says  Sir  J.  Herschel,  "  for  the  reflecting  and  scattering  power  of 
tlie  atmosphere,  no  objects  would  be  visible  to  us  out  of  direct 
sunshine,  every  shadow  of  a  passing  cloud  would  be  pitchy  dark- 
ness ;  the  stars  would  be  visible  all  day,  and  every  apartment 
into  which  the  sun  had  not  direct  admission  would  be  involved  in 
nocturnal  obscurity."  Again  to  use  the  words  of  the  same  author, 
in  speaking  of  twilight, — "  After  the  sun  and  moon  are  set,  the 
influence  of  the  atmosphere  still  continues  to  send  us  a  portion  of 
their  light  ;  not  indeed  by  direct  transmission,  but  by  reflection 
upon  the  vapours  and  minute  solid  particles  which  float  in  it,  and 
perhaps  the  actual  material  atoms  of  the  air  itself."*  Such  are 
the  beautiful  phenomena  and  the  important  results  of  the  action 
of  the  vapour  of  the  atmosphere  upon  light.  It  remains  to  men- 
tion a  few  others,  of  a  similar  character,  produced  by  the  same 
causes,  but  of  less  frequent  occurrence  and  of  less  importance  in 
the  economy  of  nature. 

The  first  of  these  minor  phenomena  which  we  shall  notice  is 
the  Mirage,  a  phenomenon  depending  partly  on  the  vapour  of 
the  atmosphere,  and  pardy  on  the  intermixture  of  strata  of  air  of 
difierent  temperatures  and  densities.  The  mirage  is  not  unfre- 
quent  in  level  countries,  when  their  surface  is  strongly  heated  by 
the  sun's  rays,  and  evaporadon  results  from  the  continuance  of 
the  heat.  The  mirage  assumes  the  appearance  of  a  sheet  of  water, 
often  exhibiting  the  reflected  or  inverted  images  of  distant  ob- 
jects. In  Egypt  and  in  the  neighbouring  sandy  plains,  where 
the  mirage  is  very  common,  the  illusion  is  at  times  so  perfect, 
that  travellers  can  hardly  be  convinced  of  the  non-existence  of 
what  they  imagine  they  see.t  The  phenomena  are  quite  expli- 
cable on  well  known  optical  principles.;}: 

Nearly  allied  to  the  mirage  is  the  appearance  termed  Fata 
Morgana,,  which  is  occasionally  witnessed  in  the  Straits  of  Mes- 
sina. There  are  many  similar  phenomena,  all  of  them  owing  to 
the  refraction  of  light  by  media  of  various  densities. 

The  next  class  of  phenomena  to  be  noticed  are  those  produced 
upon  light  by  crystals  of  ice  floating  in  the  atmosphere,  or  by 
visible  vapour.  The  angular  forms  of  the  crystals  of  ice,  by  de- 
termining the  rays  of  light  in  different  directions,  give  origin  to 
various  eccentric  halos  ;  which,  by  their  united  intensities,  par- 
ticularly where  they  cross  one  another,  occasionally  produce  con- 
spicuous masses  of  light,  denominated  parhelia  and  paraselenes, 
or  mock  suns  and  mock  moons.  Visible  vapours,  consisting  of 
water  in  the  fluid  state,  likewise  sometimes  form  halos  ;    but 

•  Treatise  on  Astronomy,  p.  33. 

f  See  Clarke's  Travels. 

^  See  WoUaston,  Philosophical  Transactions,  1800,  p. 239. 

17 


194  METEOROLOGY. 

these  halos  (when  more  than  one  exists)  are  always  concentric, 
the  sun  or  moon  being  in  the  centre.  These  two  phenomena  not 
unfrequenlly  take  place  at  the  same  time. 

The  last  and  most  frequent  phenomenon  of  the  general  kind 
■which  we  shall  notice  is  produced  by  the  action  o^  fluid  drops  of 
water  upon  light,  viz.  the  well  known  phenomenon  termed  the 
Rainbow.  The  concomitants  of  the  rainbow  are  familiar  to  every 
one  :  there  must  be  rain  along  with  sunshine.  Under  these  cir- 
cumstances if  the  spectator  turns  his  back  to  the  sun,  he  sees  the 
coloured  bow  project  on  the  opposite  cloud,  and  displaying  all 
the  tints  of  the  prismatic  spectrum. 

We  are  informed  in  the  sacred  narrative,  that  this  beautiful  phe- 
nomenon was  chosen  as  a  symbol  to  mankind  of  their  exemption 
from  future  deluge.  The  sceptic  may  be  challenged  to  state 
what  pledge  could  have  been  more  felicitous  or  more  satisfactory. 
In  order  that  the  rainbow  may  appear,  the  clouds  must  he  partial. 
Hence  the  existence  of  the  rainbow  is  absolutely  incompatible 
with  universal  deluge  from  above.  So  long,  therefore,  as  "  He 
doth  set  his  bow  in  the  clouds"  so  long  have  we  full  assurance 
that  these  clouds  must  continue  to  shower  down  good  and  not 
evil  upon  the  earth. 

3.  Of  the  Occasional  Presence  of  Foreign  Bodies  in  the  at- 
mosphere and  of  their  Effects. — The  foreign  bodies  that  occa- 
sionally exist  in  the  atmosphere  may  be  considered  as  of  two 
kinds  ;  viz.  those  which  are  merely  suspended  in  the  atmosphere 
in  a  state  of  mixture  ;  and  those  which  pervade  the  atmosphere 
in  a  state  of  solution. 

Both  in  ancient  and  in  modern  times,  and  in  various  parts  of 
the  world,  rain  and  snow  have  been  observed  to  be  coloured  by 
an  admixture  of  extraneous  matters.  The  nature  of  these  colouring 
matters  has  been  found  to  be  very  different  in  different  instances  ; 
some  have  proved  to  be  of  vegetable  origin,  consisting  of  minute 
lichens  and  other  cryptogamous  plants^  brought  from  a  distance 
by  the  agency  of  the  winds,  and  diffused  in  myriads  through  the 
atmosphere.  Such  vegetable  matters  have  been  sometimes  more 
or  less  red:  whence  those  imagined  showers  of  blood  we  read  of 
as  producing  so  much  popular  excitation.  In  other'instances  the 
colour  has  been  given  by  earthy  and  metallic  matters  in  a  state  of 
very  fine  powder,  and  in  this  case  tlieir  descent  has  been  usually 
accompanied  by  violent  electrical  phenomena,  simihir  to  those 
which  almost  always  attend  the  descent  of  Meteoric  stones  or 
Aerolites,  to  which  perhaps  they  are  nearly  allied. 

Of  the  falling  of  stones  from  the  atmosphere,  there  can  now  be 
no  doubt  ;  though  the  origin  and  the  nature  of  these  stones  are 
very  obscure,  and  indeed  cannot,  in  the  present  state  of  our 
knowledge,  be  explained.     Tliere  have  been  various  opinions  on 


FOREIGN  BODIES  IN  THE  ATMOSPHERE.  195 

the  subject.  Some,  considering  aerolites  to  be  the  productions  of 
our  own  planet,  have  viewed  them  as  masses  projected  from 
volcanoes  to  a  great  height  and  distance  in  the  atmosphere  ;  or  as 
formed  by  the  agglutination  of  the  earthy  and  metallic  powders 
from  volcanoes,  as  before  mentioned.  Others  ascribing  to  aerolites 
quite  a  different  origin,  have  viewed  them  as  fragments  scattered 
through  space,  which  happening  to  come  within  the  sphere  of  our 
earth's  attraction,  have  been  determined  to  its  surface,  (fee. 

Although  we  are  thus  uncertain  regarding  the  origin  of  aerolites, 
or  their  use  in  the  economy  of  nature  ;  it  now  seems  by  innume- 
rable observations  to  be  completely  established,  that  aerolites, 
while  in  the  higher  regions  of  the  atmosphere,  are  often  in  a 
state  of  intense  ignition.  They  there  assume  the  form  of  bril- 
liant meteors,  which  as  they  approach  the  earth,  burst  with  a 
loud  explosion,  followed  by  a  shower  of  stones.  These  stones 
generally  exhibit  evident  marks  of  fusion  :  and  many  of  them 
have  been  picked  up  while  still  warm,  so  as  to  leave  no  doubt  of 
their  being  real  aerolites,  it  is  singular  too,  that  the  composition 
of  aerolites  is  in  some  degree  peculiar.  They  invariably  con- 
tain, either  iron,  or  cobalt,  or  nickel,  or  all  these  three  metals,  in 
union  with  various  earthy  substances.  Aerolites  have  been 
found  of  every  size,  from  that  of  a  kw  grains  to  the  weight  of 
several  hundreds  of  pounds  ;  for  of  this  weight  are  some  of  those 
isolated  masses  of  iron  seen  in  different  parts  of  the  world,  and 
which  are  generally  allowed  to  be  of  meteoric  origin. 

Intermediate,  as  it  were,  between  substances  suspended,  and 
substances  dissolved,  in  the  atmosphere,  are  those  matters,  what- 
ever their  nature  may  be,  which  have  Ibeen  known  to  spread  as 
a  haze  over  large  districts,  and  have  been  termed  "  Dry  Fogs.'''' 

In  the  year  1782,  and  still  more  in  the  year  following,  a  re- 
markable haze  of  this  kind  extended  over  the  whole  of  Europe. 
Seen  in  mass  this  haze  was  of  a  pale  blue  colour.  It  was  thickest 
at  noon,  when  the  sun  appeared  through  it  of  a  red  colour.  Rain 
did  not  in  the  least  degree  affect  it.  This  haze  is  said  to  have 
possessed  drying  properties,  and  to  have  occasionally  yielded  a 
strong  and  peculiar  odour.  It  is  also  said  to  have  deposited  in 
some  places  a  viscid  liquid,  of  an  acrid  taste,  and  of  an  unplea- 
sant smell.  About  the  same  time,  there  were,  in  Calabria  and  in 
Iceland,  terrible  eardiquakes,  accompanied  by  volcanic  eruptions. 
These  earthquakes  and  eruptions  were  supposed  to  have  been 
connected  with  the  haze.  Indeed  it  has  been  generally  remarked, 
that  such  a  condition  of  the  atmosphere  has  been  usually  pre- 
ceded by  an  Ccirthquake,  either  in  the  same  or  in  some  adjoining 
countty.  The  dispersion  of  this  haze  in  the  summer  of  1783 
was  attended  by  severe  thunder  storms.  As  might  be  expected, 
the  general  stale  of  health  has,  for  the  most  part,  been  deranged 


196  METEOROLOGY. 

during  the  continuance  of  these  phenomena.  Simultaneously 
there  have  been  epidemic  diseases  of  various  kinds.  Thus,  in 
the  above  mentioned  years,  1782  and  1783,  an  epidemic  catarrh, 
or  influenza,  prevailed  throughout  Europe  ;  affecting  not  only 
mankind  but  likewise  other  animals,* 

The  nature  of  the  matter  thus  difi'used  through  the  atmosphere 
is  quite  unknown.  It  may  be  as  various  at  ditlerent  times  as  the 
character  of  the  epidemics  to  which  it  gives  origin.  As  an  ex- 
ample of  the  extraordinary  effects  which  foreign  bodies,  when 
diffused  through  the  atmosphere,  are  capable  of  producing,  we 
may  mention  those  produced  by  Selenium  when,  in  combination 
with  hydrogen,  it  is  diffused  as  a  gas  through  the  air,  even  in 
the  most  minute  quantity.  The  effects  of  this  gaseous  combina- 
tion of  selenium  with  hydrogen  are  thus  described  by  the  cele- 
brated chemist,  Berzelius,  its  discoverer.  "  In  the  first  experi- 
ment which  I  made  on  the  inhalation  of  this  gas,  I  conceive  that  1 
let  up  into  my  nostrils  a  bubble  of  gas,  about  the  size  of  a  small 
pea.  It  deprived  me  so  completely  of  the  sense  of  smell,  that  I 
could  apply  a  bottle  of  concentrated  ammonia  to  my  nose  without 
perceiving  any  odour.  After  five  or  six  hours,  I  began  to  recover 
the  sense  of  smell,  but  a  severe  catarrh  remained  for  about  fifteen 
days.  On  another  occasion,  while  preparing  this  gas,  I  became 
sensible  of  a  slight  hepatic  odour,  because  the  vessel  was  not 
quite  close  ;  but  the  aperture  was  very  small,  and  when  I  covered 
it  with  a  drop  of  water,  small  bubbles  were  seen  to  issue,  about 
the  size  of  a  pin's  head.  To  avoid  being  incommoded  with  the 
gas,  I  put  the  apparatus  under  the  chimney  of  the  laboratory.  I 
felt  at  first  a  sharp  sensation  in  my  nose  ;  my  eyes  then  became 
red,  and  other  symptoms  of  catarrh  began  to  appear,  but  only  to 
a  trifling  extent.  In  half  an  hour  I  was  seized  with  a  dry  and 
painful  cough,  which  continued  for  a  long  time,  and  which  was 
at  last  accompanied  by  an  expectoration,  having  a  taste  entirely 
like  that  of  the  vapour  from  a  boiling  solution  of  corrosive  subli- 
mate. These  symptoms  were  removed  by  the  application  of  a 
blister  to  my  chest.  The  quantity  of  Seleniuretted  Hydrogen 
Gas  which  on  each  of  these  occasions  entered  into  my  organs  of 
respiration  ivas  much  smaller  than  would  have  been  required 
of  anv  other  inorganic  substance  whatever,  to  produce  similar  ef- 
fects f't' 

As  we  have  already  stated,  selenium  is  for  the  most  part  found 
in  association  with  mineral  sulplu'h'.  Selenium  is  also,  like  sul- 
phur, a  volcanic  product.  Now,  though  we  can  hardly  imagine 
the  possibility  of  the  diffusion  of  selenium  through  the  atmo- 

*  See  article  Influenza,  in  the  Encyclopaedia  of  Practical  Medicine, 
f  Annals  of  Philosophy,  Old  Series,  vol.  xiv.  p.  101. 


EFFECTS  OF  FOREIGN  BODIES  IN  THE  AIR.         197 

sphere  in  combination  with  hydrogen  ;  selenium  may  be  so  dif- 
fused in  some  other  form  of  combination,  which  may  produce 
eilects  analagous  to  those  of  seleniuretted  hydrogen.  We  do  not 
mean  to  assert  that  the  diffusion  of  any  such  substance  really 
takes  place.  Our  intention  is  merely  to  show  that  a  small  quan- 
tity of  an  active  ingredient,  like  selenium,  is  sufficient  to  con- 
taminate the  atmosphere  over  a  wide  extent  of  country.  Such  a 
substance  being  ejected  from  the  crater  of  a  volcano  during  an 
eruption,  or  through  a  crevice  in  the  earth  during  an  earthquake, 
may  thus  produce  an  epidemic  disease.  Nor  is  it  improbable 
that  many  epidemics,  particularly  those  of  a  catarrhal  kind,  have 
so  originated. 

The  matters  occasionally  diifused  through  the  atmosphere, 
which  appear  to  be  in  a  state  of  solution.,  are  not  often  percepti- 
ble by  our  senses,  unless  in  some  cases,  perhaps,  by  the  sense 
of  smell. 

As  an  instance  of  the  presence  of  such  bodies  in  the  atmo- 
sphere we  may  mention  a  very  remarkable  observation  which  oc- 
curred to  the  writer  of  this  treatise  during  the  late  prevalence  of 
epidemic  cholera.  He  had  for  some  years  been  occupied  in  in- 
vestigations regarding  the  atmosphere ;  and  for  more  than  six 
weeks  previously  to  the  appearance  of  cholera  in  London,  had 
almost  every  day  been  engaged  in  endeavouring  to  determine, 
with  the  utmost  possible  accuracy,  the  weight  of  a  given  quantity 
of  air,  under  precisely  the  same  circumstances  of  temperature  and 
of  pressure.  On  a  particular  day,  the  9th  of  February,  1832, 
the  weight  of  the  air  suddenly  appeared  to  rise  above  the  usual 
standard.  As  the  rise  was  at  the  time  supposed  to  be  the  result 
of  some  accidental  error,  or  of  some  derangement  in  the  appa- 
ratus employed  ;  in  order  to  discover  its  cause,  the  succeeding 
observations  were  made  with  the  most  rigid  scrutiny.  But  no 
error  or  derangement  whatever  could  be  detected.  On  the  days 
immediately  following,  the  weight  of  the  air  still  continued  above 
the  standard  ;  though  not  quite  so  high  as  on  the  9th  of  February, 
when  the  change  was  first  noticed.  -The  air  retained  its  aug- 
mented weight  during  the  whole  time  these  experiments  were 
carried  on,  namely,  about  six  weeks  longer.  The  increase  of  the 
weight  of  the  air  observed  in  these  experiments  was  small  ;  but 
still  decided,  and  real.  The  method  of  conducting  the  experi- 
rnents  was  such  as  not  to  allow  of  an  error,  at  least  to  an  amount 
so  great  as  the  additional  weight,  without  the  cause  of  that  error 
having  become  apparent.  There  seems,  therefore,  to  be  only  one 
mode  of  rationally  explaining  this  increased  weight  of  the  air  at 
London  in  February,  1832  ;  which  is,  by  admitting  the  diffusion 
of  some  gaseous  body  through  the  air  of  this  city,  considerably 
heavier  than  the  air  it  displaced.     About  the  9th  of  February  the 

17* 


198  METEOROLOGY. 

wind  in  London,  which  had  previously  been  west,  veered  round 
to  the  east,  and  remained  pretty  steadily  in  that  quarter  till  the 
end  of  the  month.  Now,  precisely  on  the  change  of  the  wind 
the  first  cases  of  epidemic  cholera  were  reported  in  London  ;  and 
from  that  time  the  disease  continued  to  spread.  That  the  epi- 
demic cholera  was  the  effect  of  the  peculiar  condition  of  the  at- 
mosphere, is  more  perhaps  than  can  be  safely  maintained ;  but 
reasons,  which  have  been  advanced  elsewhere,  lead  the  writer  of 
this  treatise  to  believe  that  tlie  virulent  disease,  termed  cholera, 
was  owing  to  the  same  matter  that  produced  the  additional  weight 
of  the  air.  The  statement  of  these  reasons  here  would  be  quite 
out  of  place  :  it  is  enough  to  say,  that  they  are  principally  founded 
on  remarkable  changes  in  certain  secretions  of  the  human  body, 
which,  during  the  prevalence  of  the  epidemic,  were  observed  to 
be  almost  universal ;  and  that  analogous  changes  have  been  ob- 
served in  tlje  same  secretions  of  those,  M^ho  have  been  much  ex- 
posed to  what  has  been  termed  JMalaria.  The  foreign  body, 
therefore,  that  was  diffused  through  the  atmosphere  of  London, 
in  February,  1832,  was  probably  a  variety  of  malaria,  a  subject 
which  we  now  proceed  to  consider. 

\\\  districts  partially  covered  with  water,  and  having  a  luxuriant 
vegetation,  such  as  marshes  and  fens,  particularly  in  warm  coun- 
tries ;  or  in  colder  countries,  at  seasons  of  the  year  when  the 
sun  is  most  powerful ;  noxious  exhalations  arise,  whose  nature 
differs  perhaps  in  some  degree  according  to  the  locality.  Such 
exhalations  have  received  the  general  name  of  Malaria,  and  are 
well  known  to  be  the  fertile  source  of  various  diseases,  more  or 
less,  of  the  intermittent  febrile  type.  In  cold  and  in  temperate 
climates,  those  diseases  for  the  most  part  assume  the  character  of 
regular  ague,  or  of  rheumatism  :  but  on  approaching  to,  and  with- 
in tlie  Tropics,  they  appear  as  tlie  more  formidable  remittent  and 
continued  fevers,  tlie  well-known  scourges  of  hot  climates. 

With  respect  to  the  nature  of  these  exhalations  our  knowledge 
is  very  imperfect.  Evidently,  they  are  in  some  way  connected 
with  vegetation  ;  not  however  with  vegetation  living  and  in  a 
state  of  growth,  but  with  vegetation  in  a  state  of  decay.  It  has 
therefore  been  thought  likely  that  these  exhalations  contain  some 
gaseous  body,  composed  chiefly  of  hydrogen  and  carbon.  Their 
effect  may  arise  from  a  gaseous  compound  of  this  description, 
though  no  such  compound  is  at  present  known;  and  the  pro- 
bability is,  t-jiat  malaria  occasionally  owes  its  properties  to  other 
elements,  besides  the  hydrogen  and  carbon  disengaged  from  de- 
caying vegetables. 

We  have  thus  endeavoured  to  oive  a  concise  statement  of  that 
wonderful  assemblage  of  Laws,  of  Adaptations,  and  of  Arrange- 
ments, which  viewed  together  constitute  what  we  term  Climate; 
and  which,  as  affecting  the  welfare  of  the  denizens  of  this  globe. 


GENERAL  DESIGN  EVINCED  BY  CLIMATE.  199 

undoubtedly,  are  not  surpassed  in  interest  or  importance  by  any 
others  throughout  the  whole  of  nature.  Of  the  innumerable  suns 
and  planets  that  m.ay  occupy  the  boundless  expanse  of  the  uni- 
verse we  feel  not  the  influence  ;  even  their  existence  scarcely 
obtrudes  itself  upon  our  notice.  But  in  the  light  and  the  heat  of  our 
own  sun,  and  in  the  wind  and  the  rain  of  our  own  atmosphere,  every 
organized  being  on  this  earth,  from  Man,  the  Lord  of  its  creation, 
down  to  the  humblest  plant  that  drinks  the  dew,  is  alike  most 
intimately  concerned.  The  subject  of  Meteorology,  therefore,  in 
all  ages  and  countries,  has  attracted  the  especial  attention  of  man- 
kind. In  ruder  states  of  society  empirical  prognostics,  founded 
on  the  aspects  of  the  clouds,  on  the  movements  of  animals,  and 
on  other  incidental  occurrences,  formed  the  study  of  those  who 
pretended  to  a  foreknowledge  of  tlie  weather;  while  electrical 
phenomena  were  to  them  objects  of  superstitious  awe.  In 
modern  times  much  of  this  wonder  and  uncertainty  has  been 
removed.  The  gloom  or  the  clearness  of  the  air,  the  mists  and 
the  halos  of  a  stormy  sky,  the  restlessness  and  clamour  of  ani- 
mals, &c.,  are  now  referred  simply  to  that  overcharge  of  moisture, 
and  to  that  unequal  distribution  of  electricity  which  precede  a 
fall  of  rain.  Nay,  the  very  thunderbolt  has  been  arrested  in  its 
course,  and  from  being  no  longer  an  object  of  amazement,  has 
been  divested  of  half  its  terrors. 

But  is  this  advance  in  knowledge  calculated  to  lessen  our 
veneration  for  the  great  Author  of  nature,  or  to  derogate  from  his 
wisdom  and  his  power  ?  On  the  contrary,  our  estimate  of  both 
must  be  greatly  increased.  Of  the  Deity,  infinite  as  he  is,  and 
dwelling  in  infinity,  we  finite  beings  can  form  no  conception. 
What  little,  therefore,  we  can  know  of  Him,  we  know  nearly 
altogether  from  His  works.  Consequently  he  who  has  the  most 
studied  His  works,  will  be  the  best  qualified — nay,  will  be  alone 
qualified,  to  form  an  adequate  conception  of  Him.  Thus  to 
measure,  to  weigh,  to  estimate,  to  deduce,  may  be  considered  as 
the  noblest  privileges  enjoyed  by  man  ;  for  only  by  these  opera- 
tions is  he  enabled  to  follow  the  footsteps  of  his  Maker  and  to 
trace  His  great  designs.  Instructed  by  these,  he  sees  and  appre- 
ciates the  wisdom  and  the  power,  the  justice  and  the  benevolence 
that  reign  throughout  creation:  he  no  longer  gazes  on  the  sky 
with  stupid  wonder ;  nor  dreads  the  thunderbolt  as  manifesting 
the  wrath  of  a  vengeful  Deiiy. 

The  constituents  of  climate,  even  imperfectly  as  they  can  be 
understood  by  us,  are  seen  to  be  adjusted  and  arranged  in  a  man- 
ner so  surprising,  that  to  those  who  admit  the  existence  of  design, 
they  require  only  to  be  stated  and  apprehended,  in  order  to  their 
being  received  as  additional  proofs  of  that  great  argument.  Where 
all  are  great,  and  splendid,  and  good,  selection  is  precluded;  but 


200  METEOROLOGY, 

the  circumstances  accompanying  the  distribution  of  Water  oyer 
this  globe,  more  perhaps  than  any  other,  arrest  our  notice  as  in- 
dicative of  design.  Leaving  out  of  view  the  other  properties  of 
water ;  on  what  other  supposition,  besides  that  of  design,  can 
we  account  for  all  these  astonishing  properties  on  which  de- 
pend its  evaporation  and  diflusion  through  the  atmosphere — its 
subsequent  condensation,  not  at  once  in  tlie  form  of  water  or  of 
ice,  but  in  the  intermediate  state  of  clouds — its  colour  and  light- 
ness when  in  the  state  of  snow — its  power  of  refracting  light  and 
of  conducting  electricity — in  short,  all  the  numerous,  minute,  and 
happily  contrived  qualities  displayed  by  this  highly  elaborated 
fluid  ?  These  together  form  such  a  union  of  adaptations  and  ar- 
rangements, each  most  successfully  accomplishing  a  particular 
purpose,  and  apparently  directed  to,  and  designed  for,  that  pur- 
pose, that  to  doubt  the  agency  of  .design  would  seem  impossible. 
Yet  there  are  some  men's  minds  so  warped  that  they  either  can- 
not or  will  not  be  persuaded  of  the  existence  of  design  ;  but 
asserting  the  omnipotence  of  the  laws  of  nature,  they  forget  Him 
who  framed  these  laws,  and  are  reluctant  to  give  credence  to  His 
being  or  to  His  power.  To  such  persons  Meteorology  offers  one 
or  two  exclusive  arguments,  which,  at  the  risk  of  being  accused 
of  tediousness,  and  unnecessary  repetition,  we  shall  urge  briefly 
in  tliis  place. 

The  great  Author  of  Nature,  as  we  have  before  said,  has 
chosen  to  act  agreeably  to  certain  established  laws,  by  which  he 
is  invariably  guided.  Some  of  these  laws  we  are  able  more  or  less 
to  comprehend,  and  we  can  refer  them  to  more  general  principles. 
Others  are  beyond  our  comprehension  :  we  see  only  their  etlects ; 
and  even  these  eflects  are  most  imperfectly  revealed  to  us.  As 
instances  of  tlie  laws  of  nature  which  it  is  in  our  power  to  refer 
to  general  principles,  may  be  mentioned  the  currents  in  the  ocean 
and  in  the  atmosphere,  by  which  the  equilibrium  of  temperature 
over  tlie  globe  is  maintained.  These  currents,  we  know,  are 
strictly  referrible  to  hydrostatic  and  pneumatic  principles.  The 
argument  of  design,  which  is  deduciblc  from  these  principles,  rests, 
therefore,  not  so  much  on  the  principles  themselves,  as  on  their 
application  precisely  where  they  are  requisite.  On  the  other 
hand,  as  we  stated  at  ilie  commencement  of  this  book,  the  laws 
of  chemistry  are  founded  solely  on  experience  ;  so  that  our  ac- 
quaintance with  them  is  very  defective  ;  for  in  very  few  instances 
are  they  referrible  to  the  laws  of  quantity,  and  even  when  they 
can  be  so  referred,  it  is  only  in  a  manner  very  imperfect.  But 
though  we  do  not  comprehend  the  laws  of  chemistry,  we  see 
that  many  of  them,  perhaps  all,  in  so  far  as  they  are  intelligible 
to  us,  are  entirely  consilient  with  each  other ;  and  are  as  uniform 
in  their  operation  as  those  which  obviously  depend  on  mechanical 


GENERAL  DESIGN    EVINCED  BY  CLIMATE.  201 

principles,  or  on  the  laws  of  gravity.  Thus  the  laws,  that  all 
bodies  are  expanded  by  heat  and  are  contracted  by  cold — that 
chemical  substances  do  not  mix,  but  always  combine  in  certain 
proportions,  and  in  no  others, — are  general  laws,  to  which  there 
are  so  few  exceptions,  that  they  are  calculated  on  almost  with  as 
much  certainty,  in  the  operations  of  nature,  and  in  the  common 
intercourse  of  mankind ;  as  the  invariable  and  necessary  results, 
that  a  heavy  body  will  fall  to  the  earth,  or  that  two  and  two 
make  four.  We  have  selected  these  laws  of  chemistry  partly 
from  their  general  and  indisputable  character,  and  partly  that  the 
force  of  the  argument  which  follows  may  be  more  conspicuous: 

tdll  bodies  are  expanded  by  heat  and  contracted  by  cold.  If 
water  had  not  constituted  an  exception  to  this  law,  though  all  its 
other  properties  had  been  the  same  as  they  now  are,  long  before 
this  time,  as  we  have  seen,  half  tlie  water  on  the  globe  would 
have  been  converted  into  ice  ;  and  the  existence  of  organized 
beings  would  have  been  physically  impossible. 

*^ll  chemical  substances  combine  in  certain  proj^ortions,  and 
in  no  others.  If  air  had  been  formed  according  to  this  law,  every- 
thing else  being  the  same  as  at  present,  long  before  this  time, 
half  of  the  air  in  the  atmosphere  would  have  been  contaminated 
and  rendered  unfit  for  the  support  of  animal  life.  In  order,  there- 
fore, that  ivater  might  not  be  frozen  ;  and  that  air  might  not 
become  irrespirable ^  laws  inns t  be  infringed — and  they  are 
INFRINGED  ;  infringed  too,  precisely  where  their  infringement, 
both  in  kind  and  degree,  is  indispensably  necessary  to  organic 
existence.  Now,  we  appeal  to  the  most  inflexible  sceptic  re- 
garding the  argument  of  design,  and  ask  him,  on  what  other  prin- 
ciple, unless  that  of  express  adaptation  and  design,  can  two  such 
general  laws  have  been  infringed  exactly  in  those  instances  in 
which  their  infringement  is  wanted,  and  nowhere  else  ?  Of  the 
sophistry  by  which  the  evasion  of  this  plain  question  may  be  at- 
tempted, we  are  quite  ignorant.  But  we  cannot  resist  the  con- 
viction, that  one  purpose  of  the  arrangement  has  been  that  of 
confounding  the  presumptuous  sceptic  ;  who  is  thus  perpetually 
reminded  of  the  infringement  of  his  boasted  ""laws  of  nature," 
by  the  very  water  he  drinks,  and  by  the  very  air  he  breathes. 

With  respect  to  foreign  bodies  in  the  atmosphere,  which  have 
been  treated  of  in  the  last  section,  it  remains  to  observe,  that 
though  of  very  opposite  characters,  they  have  yet  this  resem- 
blance ;  that  they  all  apparently  exist  less  on  their  own  account, 
than  as  being  the  inevitable  results  of  general  laws  established 
for  a  higher  purpose.  Such  results  of  general  laws  may  be  con- 
sidered as  analogous  to  the  coldness  and  darkness,  which  neces- 
sarily prevail  around  the  poles,  from  the  earth's  position  in  rela- 
tion to  the  sun  ;  and  they  have  been  alike  permitted,  not  because 


202  METEOROLOGY. 

tliev  could  not  have  been  avoided  or  removed,  but  in  the  language 
of  Paley,  before  quoted,  "  because  the  Deity  has  been  pleased 
to  prescribe  limits  to  his  own  power,  and  to  work  his  ends  with- 
in these  limits." 

Man,  forgetting  how  insignificant  he  is,  and  how  limited  his 
utmost  knowledge,  is  too  apt  to  measure  Omnipotence  by  the 
standard  of  his  own  narrow  intellect,  and  to  be  guided  by  his  own 
selfish  feclincfs,  in  judo-inff  of  the  extent  of  Divine  benevolence. 
That  this  earth,  a  minute  fraction,  as  it  is,  of  a  great  and  wonderiul 
system,  should  be  amenable  to  the  general  laws  by  which  the 
whole  system  is  governed,  is,  at  the  least,  exceedingly  proba- 
ble. Of  such  general  laws,  of  their  changes,  of  their  aberra- 
tions, or  of  their  influences,  we,  situated  in  this  extremity  of  the 
universe,  cannot  see  the  object.  What,  therefore,  appears  to  us 
anomalous  or  defective,  may  in  reality  be  parts  of  some  great 
cycle  or  series,  too  vast  to  be  comprehended  by  the  human  mind, 
and  only  known  to  beings  of  a  higher  order,  or  to  the  Creator 
himself.  So  again,  amidst  the  desolation  of  the  hurricane,  or  of 
the  thunder  storm  ;  in  the  settled  ailliction  of  malaria,  and  in  the 
march  of  the  pestilence  ;  the  goodness  of  the  Deity  is  impugned, 
his  power  even,  is  regarded  doubtfully.  But  whai,  in  truth,  are 
all  these  visitations  but  so  many  examples  of  the  "  unsearchable 
ways"  of  the  Almighty  ;  "  He  sits  on  the  whirlwind,  and  di- 
rects the  storm  :"  a  hamlet  is  laid  waste  ;  a  few  individuals  may 
perish ;  but  the  general  result  is  good :  the  atmosphere  is  puri- 
fied ;  and  pestilence  with  all  its  train  of  evils  disappear.  Nay, 
however  inscrutable  the  object  of  the  deadly  malaria  itself,  do  we 
not  see  one  end  which  it  serves,  namely,  to  stimulate  the  reason- 
ing powers,  and  the  industry  of  man?  By  his  reasonf  man  has 
been  guided  to  an  antidote  beneficently  adapted  for  his  use,  which 
has  stript  malaria  of  half  its  terrors.  By  his  industry,  the  marsh 
has  been  converted  into  fertile  land,  and  disease  has  given  place 
to  salubrity. 

Wjien,  therefore,  we  duly  consider  all  these  things  ;  when  we 
reflect  also  on  the  number,  the  properties,  the  various  conditions 
of  the  matters  composing  our  globe  ;  the  wonder  surely  is,  not 
that  a  few  of  these  matters  occasionally  exist  as  foreign  bodies 
in  the  atmosphere,  but  that  others  of  these  matters  are  not  at  all 
times  (liflTused  throuirh  it,  and  in  such  quantity  as  to  be  imcompa- 
tible  with  organic  life.  Thus,  the  original  constitution  of  the  at- 
mosphere, and  the  preservation  of  its  purity  against  all  these 
contaminating  influences,  may  be  viewed  as  the  strongest  argu- 
ments we  i^ossess,  in  demonstration  of  the  benevolence,  the 
wisdom,  and  the  omnipotence  of  the  Deity  :  benevolence  in  ha- 
ving willed  such  a  positive  good  ;  wisdom  in  having  contrived  it ; 
and  omnipotence  in  having  created  it,  and  in  still  upholding  its 
existence. 


203 


CHAPTER  VI. 

OF  THE  ADAPTATION  OF  ORGANIZED  BEINGS  TO  CLIMATE  ;  COMPREHEND- 
ING A  GENERAL  SKETCH  OF  THE  DISTRIBUTION  OF  PLANTS  AND  ANIMALS 
OVER  THE  GLOBE  j  AND  OF  THE  PRESENT  POSITION  AND  FUTURE  PROS- 
PECTS OF  MAN. 

In  the  general  survey  of  climate,  and  of  its  reference  to  organ- 
ization, given  in  the  preceding  chapter,  we  have  seen,  on  the  one 
hand,  that,  by  a  series  of  wonderful  expedients,  the  climate  or 
temperature  of  the  greater  portion  of  the  earth's  surface  has  been 
so  equalized  as  to  be  brouglit  within  the  range  of  organic  exist- 
ence. On  the  otlier  hand,  we  sliall  find  that,  by  a  series  of  ex- 
pedients, no  less  wonderful,  organic  existence  has  been  so  diver- 
sified and  extended,  as  to  include  all  the  possible  varieties  of  soil 
and  climate.  Hence,  the  arrangement,  taken  altogether,  presents 
us  with  such  extraordinary  instances  of  mutual  adaptation  of  its 
various  constituents  to  each  other,  as  to  admit  of  explanation 
only  upon  the  supposition  of  the  whole  being  different  parts  of 
the  same  magnificent  Design  ;  while  the  infinite  variety,  where 
all  might  have  been  otherwise,  must  be  considered  as  equally  in- 
dicative of  the  Benevolence, and  the  Power  of  the  Designer. 

Next  to  Climate,  the  circumstances  in  which  organized  beings 
are  more  immediately  concerned  is  Soil  ;  a  subject  already  al- 
luded to,  but  which  it  will  be  necessary  to  illustrate  a  little  fur- 
ther before  we  proceed. 

The  soil  is  that  collection  of  matters,  more  or  less  in  a  state 
of  comminution,  which  immediately  covering  the  general  surface 
of  the  earth,  fills  up  its  minor  inequalities,  and  rounds  off  its 
asperities.  On  this  layer  of  comminuted  mineral  substances  and 
organic  remains,  all  vegetables  and  animals,  at  least  all  land  ani- 
mals, depend  for  their  existence ;  and,  if  there  ever  was  a  time 
when  the  materials  composing  this  globe  were  collected  into 
solid  masses,  it  is  evident  that  such  a  condition  must  have  ex- 
cluded organic  life  ;  even  if  everything  else  had  existed  the 
same  as  at  present. 

The  formation  of  the  soil  has  apparently  been  a  work  of  time, 
and  the  result  of  the  gradual  attrition  of  the  solid  materials  com- 
posing the  crust  of  this  globe.  Hence  the  formation  of  soil  has 
probably  been  al\va3'S  progressive,  and  is  still  going  on.  Besides 
this  gradual  attrition,  the  harder  materials  of  our  globe  seem  to 
have  suffered  much  disintegration  during  those  periodic  convul- 
sions formerly  mentioned.  By  the  same  convulsions,  also,  the 
different  comminuted  materials  have  evidently  been  mixed  and 


204  METEOROLOGY. 

scattered,  and  finally  deposited  over  the  surface  of  the  whole 
earth,  so  as  to  give  occasion  to  that  infinite  variety  which  every- 
where prevails. 

The  foregoing  remarks  naturally  lead  to  the  conclusion  that  the 
characters  of  the  soil  will  generally  agree  with  those  of  the  rocks 
composing  the  crust  of  tlie  earth  ;  and  this  inference  is  correct. 
The  more  common  ingredients  in  rocks  are  silex,  alumina,  lime, 
magnesia,  and  iron ;  and  these  mineral  matters  actuall}^  constitute 
the  greater  bulk  of  every  soil.  The  remaining  matters  consist  of 
more  or  less  of  various  other  earthy  and  saline  principles,  and 
of  vegetable  and  animal  remains. 

After  these  general  observations  upon  soils,  we  come  to  the 
proper  subject  of  this  chapter,  which  we  shall  consider  under  the 
three  following  sections  : — Of  the  Distribution  of  Plants  over 
the  globes — Of  the  Distribution  of  Animals  over  the  globe  ; 
and, — Of  the  present  Condition  and  future  Prospects  of  Man, 


Section  I. 
Of  the  Distribution  of  Plants  over  the  Globe, 

From  what  has  been  stated,  it  will  be  readily  understood  that 
Soil  and  Climate  are  the  two  great  and  immediate  causes  by  which 
vegetable  and  animal  existence  are  likely  to  be  affected.  We  shall, 
therefore,  in  the  first  place,  take  a  view, 

1.  Of  the  differences  of  Vegetation,  as  liable  to  be  influenced 
by  Soil,  and  by  other  minor  Loccd  Circumstances,  in  the  same 
Climate.  The  most  incurious  observer,  in  travelling  through  a 
country,  must  be  struck  with  the  different  vegetation  that  prevails 
in  different  parts  of  the  country ;  and  with  the  effect  which  this 
difference  produces  on  the  manners  and  on  the  health  of  the  in- 
habitants. Thus,  in  some  parts  of  England,  the  Apple  and  the 
Pear  are  seen  growing  spontaneously  in  every  hedge-row;  while, 
in  other  parts,  apple  and  pear  trees  will  not  flourish,  even  with 
the  utmost  care.  Some  situations  are  favourable  to  the  Oak,  others 
to  the  Beech,  others  to  the  Elm.  Accordingly,  these  well-known 
and  beautiful  trees  predominate  in  some  districts,  almost  to  the 
exclusion  of  every  other,  and  thus  constitute  the  leading  feature 
in  the  landscape. 

These  are  familiar  examples  of  partial  changes  among  the  larger 
vegetables  of  a  country;  while  the  general  vegetation  is  supposed 
to  remain  nearly  the  same.  Between  such  partial  change,  and 
the  complete  cstal)lishment  of  a  peculiar  vegetation,  there  exists 
among  dilVerent  localities,  every  possible  shade  of  diversity.  Many 
of  these  diflerences  in  vegetation  are  obviously  connected  with 


DISTRIBUTION  OF  PLANTS.  205 

difterences  in  soil  and  in  situation.  Thus,  some  plants  will  thrive 
only  on  a  calcareous  soil ;  as  a  few  of  the  Orchis  tribe  in  our  own 
country,  and  the  Teucrium  montcmum  in  Switzerland.     Others, 
like    the    Salsolas  and  the   Salicornias,  will  only  grow  in  salt 
marshes.  Some  plants  flourish  in  sea  water,  some  in  fresh;  while 
to  others  again,  water,   at  least  in  excess,  is  so  prejudicial,  that 
they  can  exist  nowhere,  unless  on  bare  rocks,  or  in  arid  deserts. 
Mountainous  situations  are  most  favourable  to  the  increase  of  some 
plants,   while  others  abound  in  plains.     The   larger  number  of 
plants  prefer  sunshine,  but  some  are  most  vigorous  in  the  shade  ; 
and  others  are  so  impatient  of  light,  that  they  are  found  only  where 
there  is  absolute  darkness.     There  are,  besides,   parasitic  plants, 
like  the  Mistletoe,  whose  nourishment  is  derived  from  the  plants 
to  which  they  are  attached.     In  short,  the  varieties  in  the  nature 
of  plants  are  countless,  nor  is  the  enumeration  of  them  requisite. 
What  has  been  stated  is  more  than  enough  to  show  the  wonder- 
ful arrangements  that  have  been  made,  to  ensure  the  clothing  of 
every  part  of  the  earth's  surface  with  vegetable  organization.  There 
is  not  a  soil,  however  barren,  nor  a  rock,  however  flinty,  that  has 
not  its  appropriate  plant;   which   plant  has  no  less  wonderfully 
found  its  way  to  the  spot  adapted  for  it,  nay,  will  perish  if  removed 
elsewhere.     Saline  plants,  for  instance,  will  grow  only  where  sa- 
line matters  are  abundant;  plants  of  the  marsh,  and  of  the  bog, 
flourish  only  in  marshy  and  boggy  ground  ;  those  of  the  parched 
desert  and  of  the  cloudy  mountain,  each  in  its  fitting  locality. 
Thus  the  soil  and  its  occupant  seem  to  have  been  made  for  each 
other  ;  and  hence  one  source  of  that  astonishing  variety  exhibited 
in  nature. 

There  are  still  more  remarkable  deviations  among  the  plants 
of  different  countries  remote  from  one  another;  even  where  the 
circumstances  of  climate  and  of  soil  are  in  every  respect  alike. 
The  plants  of  the  Cape  of  Good  Hope,  for  instance,  diff'er  exceed- 
ingly from  those  of  the  south  of  Europe,  though  the  climate  and 
much  of  the  soil  be  not  dissimilar.  Often,  on  the  same  continent, 
nay,  on  the  same  ridge  of  mountains,  the  plants  on  the  opposite 
sides  have  no  resemblance.  "  Thus,  in  North  America,  on  the 
east  side  of  the  rocky  mountains,  Azaleas,  Rhododendrons,  Mag- 
nolias, Vacciniums,  Aciseas,  and  Oaks,  form  the  principal  features 
of  the  landscape;  while  on  the  western  side  of  the  dividing  ridge, 
these  genera  almost  entirely  disappear,  and  no  longer  constitute  a 
striking  characteristic  of  the  vegetation."* 

In  general,  the  plants  of  America  are  diflerent  from  those  of 
the  old  world,  except  towards  the  north,  where,  as  it  might  be 
expected  from  the  near  approximation  of  the  two  continents,  many 
individuals  are  common  to  both.  The  plants  of  islands,  and  those 

*  Lindley's  Introduction  to  Botany,  page  489. 

18 


206  METEOROLOGY. 

growing  in  isolated  situations  are  often  quite  peculiar.  Tlius  the 
plants  of  New  Holland,  with  comparatively  few  exceptions,  differ 
froin  those  of  all  the  rest  of  the  world  ;  and,  "of  sixty-one  native 
species,  in  the  little  island  of  Saint  Helena,  only  two  or  three  are 
to  be  found  in  any  other  part  of  the  globe."*  These  facts  are  quite 
inexplicable  upon  any  known  principles  ;  and  are  calculated  to 
excite  a  more  than  ordinary  degree  of  attention,  as  being  solely  re- 
ferrible  to  the  will  of  the  Great  Creator;  who  has  chosen  to  pro- 
vide infinite  diversity  where  all  might  have  been  uniform  and 
monotonous ;  and  has  thus  rendered  more  conspicuous  his  wisdom, 
his  power,  and  his  goodness. 

2.  Of  the  Influence  of  Climate  on  Vegetation. — The  climate 
of  a  place,  as  has  been  before  shown,  independently  of  minor  lo- 
cal causes,  is  influenced  chiefly  by  the  two  following  circum- 
stances:— the  Latitude  of  the  place  ;  in  other  words,  the  general 
portion  of  heat  and  light  which  it  receives  from  the  sun  ; — and  its 
height  above  the  surface  of  the  sea  ;  by  which  circumstance  of 
elevation,  the  heat  at  least  received  from  the  sun,  is  liable  to  be 
varied  as  much  as  by  latitude ;  but  the  variation  is  according  to 
other  laws  than  those  which  depend  on  mere  latitude,  indeed,  ac- 
cording to  laws  which  vary  in  diflerent  latitudes. 

Every  one  is  acquainted  with  the  general  fact  of  the  difference 
between  the  plants  of  warm  and  those  of  cold  countries  ;  between 
the  plants  that  grow  on  plains,  and  those  that  grow  on  mountains. 
Thus,  "  in  the  countries  lying  near  the  Equator,  the  vegetation 
consists  of  dense  forests  of  leafy  evergreen  trees,  Palms,  apd  ar- 
borescent Ferris,  among  which  are  intermingled  epiphytal  herbs, 
and  rii^id  Grasses.  There  are  no  verdant  meadows,  such  as  form 
the  chief  beauty  of  our  northern  climate,  and  the  lower  orders  of 
vegetation,  such  as  Mosses,  Fungi  and  Confervfe  are  very  rare. 
As  we  recede  from  tiiC  Equator,  the  plants  above  mentioned  gra- 
dually give  way  to  trees  with  deciduous  leaves  ;  rich  meadows 
appear,  aboundmg  with  tender  herbs;  the  epiphytal  Orchideie  are 
no  longer  met  with,  and  are  replaced  by  terrestrial  fleshy-rooted 
species  ;  Mosses  clothe  the  lrun!;s  of  aged  trees  ;  decayed  vegeta- 
bles are  covered  with  parasitical  Fungi  ;  and  the  waters  abound 
with  Corfervx.  Approaching  the  Poles,  trees  wholly  disappear; 
dicotyledonous  plants  of  all  kinds  become  comparatively  rare  ; 
and  Grasses  and  cryptogamic  plants  constitute  the  chief  features 
of  the  vegetation."! 

(Changes  not  very  dissimilar  are  observed  in   the  vegetation  at 
diflcrent  heights  on  the  mountains  of  warm  climates-     Thus,  at 

•  See  Principles  of  Geolog-y,  by  C.  Lyall,  vol.  ii.  where  this  interesting" 
subject  is  considered  in  detuil. 

■j-  Lindley's  introduction  to  Botany,  pug^e  484. 


DISTRIBUTION  OF  PLANTS.  207 

the  base  of  the  celebrated  Peak  of  Teneriffe,  the  plants  have  all 
the  disliniruishinof  characters  of  those  of  Africa.  Tfiere  flourish 
the  succulent  Euphorbia,  the  Mesemhryanthenia,  Draccvna^  &;c. : 
also  the  Dale  pahn,  the  Plantain,  the  SuQ;ar-cane,  and  the 
Indian-Jig.  A  little  higher,  grow  the  Olive  tree^  the  fruit  trees 
of  Europe,  the  Vine,  and  Wheat.  Then  succeeds  the  woody 
region  of  the  mountain  ;  where  from  the  numerous  springs  the 
ground  is  always  verdant.  In  that  region  is  seen  a  profusion  of 
beautiful  evergreens  :  such  as  various  species  of  Laurel,  one  of 
Oak,  two  species  of  Iron  tree,  an  Arbutus,  and  several  others. 
Next  above  is  the  region  of  pines,  characterized  by  a  vast  forest 
of  trees  resembling  the  Scottish  fir,  intermixed  with  Jumper. 
Then  follows  a  tract  remarkable  for  the  abundance  of  a  species  of 
broom.  At  last  the  scenery  is  terminated  by  Scrqfularia,  Violas 
a  few  Grasses,  and  cryptogamic  plants.* 

The  proportions  which  different  groups  of  plants  bear  to  each 
other,  vary  exceedingly  in  different  latitudes.  An  interesting  table 
given  in  the  Appendix,  slightly  altered  from  Humboldt,  exhibits 
the  proportional  amount  of  some  natural  groups  of  plants  to  the 
whole  mass  of  vegetation  in  the  zones  mentioned  ;  and  will  enable 
the  reader  to  understand  the  relation  of  vegetable  forms  to  the 
greater  or  less  distance  of  their  place  of  growth  from  the  Equator. 
The  arrangement  is  so  obvious  as  scarcely  to  require  explanation. 
Thus  in  the  equatorial  zone,  between  10°  north  and  10°  south 
latitude,  the  first  group,  including  Ferns,  Lichens,  Mosses,  and 
Fungi,  constitutes  on  the  plains  only  1-1 5th,  but  on  the  moun- 
tains l-5th  of  the  whole  number  of  plants  that  exist  in  that  zone. 
While  in  the  temperate  zone  the  proportion  of  the  tirst  group  of 
plants  is  at  least  one-half  of  the  whole  number,  and  in  the  frigid 
zone,  the  entire  vegetation  consists  of  plants  of  that  group.  The 
distribution  of  the  other  groups  is  equally  remarkable. 

From  this  table  we  learn  many  interesting  particulars  in  addi- 
tion to  what  has  been  already  stated  regarding  the  distribution  of 
plants  over  the  surface  of  the  globe.  We  may  notice  especially 
the  striking  difference  between  the  Flora  of  the  Old  and  that  of 
the  New  World,  in  corresponding  parallels  of  latitude.  These 
differences,  in  a  great  many  instances,  are  undoubtedly  referrible 
to  the  unknown  causes  to  which  we  have  before  alluded.  But 
in  other  instances,  they  are  obviously  connected  with  the  differ- 
ence of  temperature  that  prevails  in  the  two  continents  under  the 
same  parallel.  Before  we  proceed,  let  us  dwell  a  little  longer  on 
the  consideration  of  these  beautiful  arrangements. 

In  Tropical  countries  alone,  beneath  a  vertical  sun,  do  we  see 
vegetation  in  all  its  glory  and  magnitude.     There,  the  form,  the 

*  Humboldt. 


208  METEOROLOGY. 

colour,  and  the  odour  of  plants  are  developed  to  the  utmost;  and 
wliere  else  could  they  be   so  developed  ?   where    else   could  the 
majestic  palm  rear  its  towering  stem,  and  send  forth  its  gigantic 
leaves  ?  where  else  could  we  expect  to  find  groves  ever  verdant, 
blooming  and  productive  ?     Amidst  eternal  summer,  all  this  is  in 
character ;  forests  denuded  of  their  leaves,  and  for  half  the  year 
assuming  the  appearance  of  deatli,  would   in  such  a  climate  be 
perfectly  incongruous.     But  in  countries  remote  from  the  Equa- 
tor, and  in  which,  during  many  months,  the  temperature  is  more 
or  less  depressed,  a  vegetation  tlius  incessantly  active  could  not 
exist  nor  would  it  be  appropriate.     Accordingly,  the  palm  tribe, 
and  many  of  the  more  distinguishing  productions  of  the  Tropics 
become    gradually    fewer    irj   number   as    we   recede    from    the 
Equator,    and    at   last    give  way  entirely  to  deciduous   plants  ; 
that  is,  to  plants  endued   with   the    power  of   hybernating,  or 
sleeping,  as  it  were,  in  the  colder  season  ;  and    which   vegetate 
only  during  the  warmer  portion  of  the  year.     And  here  we  have 
displayed  another  of  those  admirable  provisions,  which   at  once 
strike  us  irresistibly  as  being  the  effect  of  design  !     In  Tropical 
countries,  where  the  seasons  are  uniform,  and  where  there  is  no 
cold  to  injure,   the   leaf  buds  of  plants  are  without   covering  or 
protection,  and  are  freely  and  confidently  exposed  to  the   atmo- 
sphere.    But  in  climates  where  the  seasons   change,  and  where 
vegetation  is  liable  to  be  suspended    by  the  cold,  the   leaf  buds 
exhibit  a  structure  remarkably  different.     Developed  in  the  latter 
end  of  summer,  or  autumn,  they  are  almost  invariably  provided 
with  tegmenta  or  coverings  ;   within  which,  during  their  period 
of  torpor  they  are  cradled,  safe  from  cold  and  from  accident ! 

As  we  advance  still  further  to  the  north  or  to  the  south,  where 
the  winter  becomes  more  severe  and  of  longer  continuance,  decidu- 
ous plants  in  their  turn  diminish  both  in  number  and  in  magnitude  ; 
and  after  having  shown  themselves  under  a  variety  of  stunted 
forms,  are  at  length  almost  entirely  superseded  by  a  few  coarse 
grasses  and  lichens.  Yet  even  here  design  is  apparent.  These 
hardy  natives  of  the  poles  are,  from  the  simplicity  of  their  struc- 
ture, wonderfidly  adapted  to  tlie  climate  of  the  region  they  occupy  ; 
in  which  alone  they  will  flourish,  and  for  which  alone,  therefore, 
ihey  have  been  expressly  created. 

Though  it  be  generally  true  that  plants  will  grow  only  in  the 
soil  and  climate  adapted  for  them  ;  yet,  as  if  intentionally  to 
evince  His  power,  the  Great  Author  of  nature  has  created  some 
manifci^t  exceptions  to  this  rule.  All  organized  beings  have  been 
nunc,  or  less  endowed  with  the  faculty  of  accommodating  them- 
selves to  circumstances.  In  the  larger  number  of  plants  this 
faculty  scarcely  exists;  but  in  some  it  is  much  stronger;  and  in 
others,  constituting  the  exceptions  to  which  we  allude,  the  extent 


DISTRIBUTION  OF  PLANTS.  209 

of  the  accommodating  faculty  is  almost  incredible.     In   general, 
plants  that  are  the  natives  of  peculiar  soils,  and  of  extreme  cli- 
mates, are  the  most  impatient  of  change  ;  while   the  natives  of 
ordinary  soils,  and  of  temperate  climates,  have  a  wider  range  of 
growth.     The  exceptions  to  the  rule  of  adaptation   are  ciiiefly 
among  plants  that  are  natives  of  such  soils  and  climates.     Thus 
**  the   Sa7nolu8  Valerandi  is  found  all  over  the  world,  from  the 
frozen  north  to  the  burning  south  ;  associated  here  with  Birches^ 
and  similar  northern  forms,  and  there  mixed  with  Pahns  and  the 
genuine  denizens  of  the  tropics.     The  number  of  plants,  how- 
ever, which  can  thus  accommodate  themselves  to  all  circumstances 
and  climates   is  limited  ;   while  those  which   readily  naturalize 
themselves  in  climates  similar  to  their  own,    are,   on   the  other 
hand,  numerous.     Of  the  latter,  indeed,  examples  present  them- 
selves at  every  step.     All  the  hardy  plants,  for  instance,  of  our 
gardens   may   in  some  sort   be    considered  of  this    nature ;  for 
although    they  do  not  grow   spontaneously  in    the   fields,  they 
flourish  almost  without  care  in  our  gardens.     The  Pine  apple  has 
gradually  extended  itself  eastward  from  America,  through  Africa, 
into  the  Indian  Archipelago,  where  it  is  now  as  common  as  if  it 
were  a  plant   indigenous    to  the   soil  ;  and   in  like  manner  the 
Spices  of  the  Indies  have  become   naturalized   on    the   coast  of 
Africa  and  the  West  India  islands."    To  this  property  of  natural- 
izing themselves,  no  doubt,   is  to  be  referred,  in  a  variety  of  in- 
stances, the  presence  of  the  same  plants   in   different  countries. 
For  though,  as  we  have  just  stated,  the  Flora  of  different  countries 
is  generally  different,   yet  in  almost  all  instances,   some   plants 
exist  which  are  found   in   other  countries.     Thus,  "above  350 
species  are  said  to  be  common  to  Europe  and   North  America; 
and  even  among  the  peculiar  features  of  the  Flora  of  New  Hol- 
land,   Mr.    Brown   recognized    166    European    species.      The 
presence  of  many  such  strangers  may  undoubtedly  be  referred  to 
the  agency  of  man  and  other  animals  ;  to  currents   in  the  ocean, 
to  winds,  and  a  variety   of  natural   causes."     While   "  the  pre- 
sence of  others,  seems  inexplicable  on  any  other  supposition  than 
that  they  have    been    created   in   the  places   where  they    now 
exist."* 

Hitherto  we  have  considered  plants  only  in  relation  to  the  soil 
and  to  the  climate  in  which  they  grow  ;  and  have  not  entered  into 
details  respecting  all  the  beautiful  arrangements,  by  which  their 
growth  has  been  accomplished.  The  consideration  of  these 
arrangements  belongs  to  the  Physiologist,  the  Botanist,  and  the 
Geologist,  wdth  whose  duties  we  wish  as  little  as  possible,  to  in- 
terfere.    There  is,  however,  yet  one  point  of  view  in  which  our 

*  Lindley,  Introduction  to  Botany,  p.  501. 
18* 


210  »  METEOROLOGY. 

argument  nalurally  leads  us  to  consider  vegetation  ;  namely,  as 
forming  the  link,  by  which  animals  are  connected  with  the  earth  ; 
in  other  words,  as  furnishing  to  animals  the  means  of  subsist- 
ence. 

One  circumstance,  which,  perhaps  more  than  any  other  is  cal- 
culated to  arrest  our  attention  with  respect  to  vegetable  produc- 
tions in  general,  is  their  vast  profusion  in  every  sense  of  the 
term  ;  whether  we  contemplate  their  variety,  their  magnitude,  or 
their  number.  Tlius  the  numerous  and  varied  plants  growing  in 
tropical  climates  are  equally  remarkable  from  their  size,  the  luxu- 
riant foliage,  and  the  exuberance  of  their  roots  and  seeds.  Let  us 
take,  for  instance,  the  palm  tribe.  It  has  been  estimated  that 
there  are  a  thousand  species  of  palms  ;  and  though  the  number 
actually  known  to  exist  is  by  no  means  so  large,  yet  late  disco- 
veries seem  to  render  the  estimate  not  improbable.  In  many  of 
the  palm  tribe  the  developement  of  the  form,  and  the  quantity  of 
flowers  and  fruit  is  altogether  extraordinary.  Among  others,  the 
species  which  yields  the  well  known  Cocoa  nuts  grows  to  the 
height  of  eighty  feet ;  each  plant  flourishes  for  a  century,  and, 
during  the  greater  part  of  that  lime,  continues  to  produce  an- 
nually at  least  a  hundred  of  these  large  nuts.  Yet  the  cocoa  nut 
species  may  be  considered  as  one  of  the  least  productive  of  the 
palm  tribe  :  for  every  bunch  of  another  species,  the  Seje  palm 
of  the  Oronoko,  bears  as  many  as  8000  fruit ;  while  a  single 
spatha  of  the  Date  palm  contains  12,000  flowers  ;  and  in  a  third 
species,  the  .'ilfonsia  Ainyis;daHna,  there  is  the  enormous  num- 
ber of  207,000  flowers  on  each  spatha  ;  or  000,000  on  a  single 
individual  plant  ! 

In  superlative  exuberance,  however,  the  Palm  tribe  must  yield 
to  the  Jianana,  or  Plantain,  another  inhabitant  of  tropical  coun- 
tries, 'i'he  fruit  of  this  plant  is  often  a  foot  in  circumference,  and 
seven  or  eight  inches  long:  it  is  producetl  in  bundles,  containing 
usually  from  160  to  180  fruit;  and  each  bunch  weighs  from  06 
to  88  pounds  avoirdupois.  As  Humboldt  has  remarked  ;  the 
small  space,  therefore,  of  1000  square  feet,  on  which  from  thirty 
to  forty  Banana  plants  may  grow,  will,  on  a  very  moderate  com- 
putation afford,  in  the  course  of  a  year,  4000  pounds  weight  of 
fruit  ;  a  produce  133  times  greater  than  could  be  obtained  from  the 
same  space,  if  covered  with  wheat;  and  44  times  greater  than  if 
occupied  by  potatoes.  'J'lie  Orange  tree  may  be  mentioned  as 
another  instance  of  extraordinary  fecundity  ;  thus  a  single  tree  at 
St.  Michael's  has  been  known  to  bear  in  a  season  20,000  oranges 
lit  for  parking,  exclusively  of  those  damaged  and  wasted,  amount- 
ing to  at  least  one-third  more.  An  example  to  the  same  eflect, 
but  of  a  diflerent  kind,  is  the  Sugar  cane,  which  furnishes  an 
unlimited  supply  of  saccharine  matter  in  its  purest  form  ;  while 


DISTRIBUTION  OF  PLANTS.  211 

various  roots,  as   those  of  the  Cycas  Jatropa,  and  many  others 
abound  equally  in  farinaceous  matters. 

As  we  withdraw  from  the  Equator  into  the  regions  of  hyber- 
nating  plants,  vegetation  is  seen  on  a  much  less  magniiicent 
scale  ;  though  in  the  temperate  climates,  and  even  where  we 
might  expect  to  find  utter  sterility,  mimber,  in  some  degree,  com- 
pensates for  magnitude.  Thus,  instead  of  the  single  stupendous 
tuft  of  the  palm,  we  have  the  numerous  congregated  buds  of  our 
deciduous  trees  ;  instead  of  the  gigantic  and  solitary  grasses  of  the 
torrid  zone,  we  have  the  smaller  and  gregarious  varieties.  Some 
of  these  varieties,  as  the  Cerealla,  or  Corn  tribe,  with  their 
myriads  of  seeds,  give  us  an  inexhaustible  supply  of  farinaceous 
aliment ;  while  others,  as  the  Grasses  properly  so  called,  clothe 
our  meadows  with  verdure,  even  to  extreme  latitudes  ;  and  are 
equally  productive  of  matter  purely  herbaceous.  In  the  warmer 
parts  of  the  temperate  zone,  the  Olive  and  the  Vine  afford  the 
oleaginous  and  the  saccharine  principles  under  a  form,  different, 
but  not  less  useful  than  the  oil  and  the  sugar  of  the  tropics  ; 
while  in  the  colder  parts,  various  seeds,  and  hardy  fruits,  produce 
an  ample  store  of  the  same  valuable  articles,  though  in  a  condi- 
tion still  further  modified. 

In  the  preceding  sketch  we  have  intentionally  kept  out  of  view 
the  existence  of  animals,  that  we  might  here  ask  the  question, 
Of  what  use  is  all  this  amazing  exuberance  of  superfluous  matter 
throughout  the  globe  ?  The  adaptation  of  plants  to  the  climates 
in  which  they  flourish  is  evidently  the  work  of  an  intelligent 
Creator.  But  is  this  apparent  waste  of  materials  and  of  labour  to 
be  reconciled  with  the  same  wise  agency  ?  Surely,  the  mere  ex- 
istence of  vegetation  did  not  require  such  prodigality.  Seeds,  for 
instance,  need  not  have  been  enveloped  in  bulky  fruits  ;  nor  need 
they  have  been  produced  by  myriads  :  and  all  that  foliage,  all 
those  flowers,  and  roots,  in  such  amazing  profusion,  of  what  use 
are  they  ;  why  where  they  so  created?  Regarding  vegetation  as 
a  thing  simply  adapted  to  climate,  and  existing  for  its  own  sake 
alone,  the  question  scarcely  admits  of  a  rational  answer.  But, 
considering  at  the  same  time  the  existence  of  animals,  and  view- 
ing these  superfluities  as  the  means  by  which  animal  existence 
is  principally  upheld,  every  difficulty  vanishes,  and  the  splendid 
design  of  the  whole  wonderful  scheme  becomes  at  once  apparent. 
We  are  thus  brought  to  the  consideration  of  animal  existence. 


•^l2  METEOROLOGY. 

Section  II. 
Of  the  Distribution  of  ^^nimals  over  the  Globe. 

Animals  have  been  so  conslituled  that  food  is  to  them  indis- 
pensable :  they  can,  therefore,  exist  only  where  their  food  has 
been  supplied  by  nature.  On  land,  at  least  in  the  warm  and  tem- 
perate climates,  by  far  the  greater  proportion  of  animals  derive 
their  subsistence,  either  directly  or  indirectly,  from  the  vegetable 
kingrdom.  For  those  animals  that  are  themselves  carnivorous, 
prey  on  vegetable  feeders  much  ofiener  than  otherwise  ;  and  are 
thus  remotely  dependent  on  vegetables.  Of  the  habits  of  animals 
livincr  ill  the  sea,  and  thus  concealed  from  our  view,  we  know 
still  less  ;  but  in  general  they  appear  to  prey  on  each  other,  the 
stronger,  as  is  usual,  devouring  the  weaker. 

We  have  seen  the   wonderful  diversities  that  prevail  among 
vegetables,  in  different  situations  and  climates  ;  and  it  may  be 
truly  said  that  tlie  diversities  among  animals  are  not   less  nume- 
rous, and  are  even  more  extraordinary.      Thus,  in  every  climate 
and  soil,  almost  every  herb  has  its  appropriate  inhabitant  ;  some 
little  being,  that  comes  into  existence,  passes  its  ephemeral   life, 
and  dies  on  that  plant ;   to  which,  therefore,  that  plant  constitutes 
the  world.      Nay,  in  general,  even  different  parts  of  the  same 
plant  have  each  its  separate  occupants,  one   feeding  on  its   fruit, 
another  on  its  flowers,  a  third  on  its  leaves,  perhaps  a  fourth  on  its 
very  woody  core.     This  almost  infinite  diversity,  and  infinity  of 
number,  are  principally  confined  to  the  smaller  animals,  or  insects. 
As  animals  increase  in  size,  the  number  of  species  as  well  as  of  in- 
dividuals constantly  diminishes.  Thus,  while  there  are  hundreds  of 
species  of  the  Beetle  tribe,  and  the  individuals  are  counUess,  there 
may  be  considered  to  be  only  one  Elejdiant;  and  while  Shrimps  are 
in  numbers  like  the  sand  on  the  sea-shore,  the  Whale  is  as  much 
a  solitary  species.     This  striking  dilierence  with  reffard  to  num- 
bers  has  been  considered  to  arise  necessarily  from  a  law  of  nature, 
and  in  one   respect  such  an  explanation  is  very  obvious  ;  but  in 
another  point  of  view,  we  may  contemplate  an  admirable  evidence 
of  design.     It  is  clear  that  millions  of  elephants  could  not  exist, 
if  for  no  other  reason,  from  want  of  food  ;    but  why  should  ruil- 
lions  of  beetles  exist  ?   why  should  these  little  creatures, — whose 
life  is  so  transitory,  that  it  consists  of  little  more  than  of  being 
born,  and   of  dying,  whose  structure   is  so  frail  as  to  be  liable  to 
be  annihilated  by  the  slightest  accident,  who  are  everywhere  sur- 
rounded by  all  sorts  of  enemies,  to  many  of  which  they  constitute 
a  natural  prey, — why,  we  ask,  in  spite  of  all  these  obstacles  and 
dangers,  should  these  insignificant  animals  contrive  to  exist  in 


DISTRIBUTION  OF  ANIMALS.  213 

the  numbers  we  see  them  ?  No  natural  law,  surely,  will  explain 
tiie  appearance  of  such  multitudes.  The  difficulty  requires  another 
solution  ;  and  the  only  solution  that  can  be  offered  is  design — 
that  it  was  so  designed  by  the  Great  Author  of  nature.  And  how 
has  He  effected  His  purpose  of  multiplying  to  such  an  extent 
these  little  animals  ?  The  answer  is,  simply,  by  increasing  their 
fecundity.  Had  beetles,  like  elephants,  brought  forth  only  one 
young  at  a  time,  long  ere  now,  their  race  would  have  been  ex- 
terminated ;  but  being  produced  by  thousands,  some  of  the 
numerous  offspring  chance  to  escape,  and  thus  the  race  is  per- 
petuated. 

We  shall  not  dilate  further  on  the  arrangements  that  have  been 
made  for  the  existence  and  preservation  of  animals,  but  shall  pro- 
ceed to  consider  their  distribution. 

The  distribution  of  animals  over  the  globe  may  be  conveniently 
treated  of  under  the  same  heads  as  the  distribution  of  vegetables  ; 
and,  first:  — 

1.  Of  the  Differences  existing  among  Jinimals  that  live  in 
similar  Situations  in  different  Parts  of  the  World. — The  dwell- 
ing of  animals  in  the  waters  is,  perhaps,  the  most  remarkable  as 
regards  their  localities.  Now,  since,  from  circumstances  formerly 
staled,  the  distribution  of  temperature  is  very  different  in  the  sea 
from  what  it  is  on  land  ;  and  since  most  aquatic  animals  prey  on 
each  other,  and  consequently  in  some  degree  are  independent  of 
climate  ;  the  distribution  of  such  animals  over  the  globe  follows 
laws  materially  different  from  those  wliich  regulate  the  distribu- 
tion of  land  animals.  This  distribution  of  temperature  more 
especially  affects  the  distribution  of  animals  in  high  latitudes  ;  and 
must  be  taken  into  account  at  the  very  outset  of  this  part  of  our 
inquiry.  We  shall,  therefore,  state  concisely  the  distribution  of 
land  animals,  and  of  sea  animals,  apart  from  each  other. 

The  distribution  of  land  animals  resembles  to  a  certain  extent 
that  of  vegetables  ;  for  though  animals  differ  from  plants,  in  being 
endowed  with  the  power  of  locomotion,  yet,  as  the  larger  number 
of  animals  are  dependent  on  vegetables  for  their  subsistence,  they 
are  necessarily  confined  to  those  places  where  their  peculiar  food 
may  be  obtained.  This  limitation  of  range  is  most  observable  in 
the  case  of  the  smaller  animals.  The  existence  of  many  kinds 
of  insects,  especially,  is  intimately  connected  with  that  of  certain 
plants.  In  every  tribe  of  animals,  however,  there  are  species 
that  occupy  very  different  localities.  Thus,  in  the  same  tribe, 
some  species  dwell  on  the  mountains,  others  on  the  plains;  some 
are  most  numerous  on  the  sea-coast,  others  live  on  trees,  while 
there  are  others  that  burrow  beneath  the  surface  of  the  ground. 
All  these  diversities,  in  regard  to  residence,  are  probably  influ- 
enced, like  many  others,  by  the  greater  or  less  degree  in  which 


214  METEOROLOGY. 

the  locality  affords  the  means  of  obtaining  subsistence.  But,  in 
many  animals,  there  is  also  a  wonderful  adaptation  of  structure  to 
the  place  ihey  inlrabit ;  proving,  beyond  a  doubt,  that  the  distri- 
bution of  animals  has  been  arranged  by  design ;  and  that  they 
form  but  a  part  of  the  great  symmetrical  whole  of  creation. 

In  animals  that  dwell  in  the  water,  the  same  peculiarities  of 
habitude  are  observable,  as  in  those  that  dwell  on  the  land.  Thus, 
it  is  perfectly  known  that  many  animals  can  live  only  in  salt  wa- 
ter;  others  only  in  fresh.  Some  prefer  the  deep  and  open  sea, 
others  are  met  with  only  in  shallow  water,  or  at  the  mouths  of 
rivers.  Of  those  that  flock  to  the  coast,  some  shun  turbid  water, 
others  burrow  in  the  mud.  In  short,  though  the  habits  and 
adaptations  of  aquatic  animals  can  be  less  satisfactorily  ascer- 
tained ;  there  is  every  reason  to  believe  that  they  are  at  least  as 
wonderful,  as  those  of  the  occupants  of  the  land. 

There  is  an  equally  striking  diversity  in  the  animals,  as  in  the 
plants,  of  similar  localities  and  climates  in  different  parts  of  the 
world.  Thus,  in  the  old  world,  in  the  analogous  climates 
on  the  north,  and  on  the  south  of  the  equator,  though  many  ge- 
nera exist  in  common,  yet  the  species  are  totally  different.  For 
instance,  the  northern  hemisphere  possesses  the  Horse,  and  the 
Jiss  ;  while,  in  the  south,  these  species  are  represented  by  the 
Zebra  and  the  Quags:a.  In  the  southern  hemisphere,  there  also 
exist  many  species  which  are  qiiite  peculiar;  as  the  GlraJ/e,  the 
Cape  Buffalo,  and  a  variety  of  animals  having  the  Jintelope  form. 
So,  likewise,  the  animals  of  the  old  and  those  of  the  new  world 
are,  in  general,  quite  distinct ;  unless,  perhaps,  towards  the  north, 
where  the  two  continents  approximate;  and  where,  in  conse- 
quence, there  are  some  species  common  to  both.  Thus  the  Eh- 
phant,  the  Rhinoceros,  the  Hippopotamus,  the  Giraffe,  the  Camel, 
the  /Jromcdurif,  the  Horse  and  the  ^^ss  ;  also  the  Lion  and  the 
Tif^er,  and  various  species  o{  Apes,  Baboons,  and  other  animals, 
with  which  we  are  familiar  in  the  old  world,  were  not  found  in 
America.  On  the  other  hand,  the  American  species,  the  Lama, 
and  the  Feccari ;  and  among  carnivorous  animals,  the  Jaguar, 
or  American  tiger;  also  the  Jlgouti,  tlie  Paca,  the  Coati,  the 
Sloth,  and  others,  were  equally  unknown  in  the  old  world. 
Again,  the  animals  of  New  Holland  differ,  like  its  vegetation,  not 
only  from  all  those  of  our  continent,  but  from  those  of  all  the 
world  besides.  In  New  Holland,  there  are  more  than  forty  spe- 
cies of  marsupial  or  pouched  animals,  of  which  the  Kangaroo  is 
that  with  which  we  liave  become  best  acquainted  ;  while  every- 
where else,  there  is  hardly  a  known  instance  of  a  pouched  animal. 
Nor  are  these  diff«*rences  confined  to  the  more  perfect  animals. 
They  are  even  more  striking  as  we  descend  in  the  zoological 
scale,     'i'hus  among  birds  ;  the  individual  species  of  the  Parrot 


DISTRIBUTION  OF  ANIMALS.  215 

tribe,  that  are  found  in  America,  differ  altogether  from  those  of 
Africa  ;  and  those  of  Asia  differ  from  both.  The  minute  and 
beautiful  family  o(  Hutmnhig  birds  is  peculiar  to  America.  While 
the  species  of  the  common  Grouse  of  this  country  is  met  with 
in  no  other  part  of  the  known  world. 

From  the  class  of  reptiles,  may  be  mentioned  the  Great  Saurian, 
or  Lizard  tribe.  Thus  the  Crocodile  of  the  Nile  is  entirely  dif- 
ferent from  the  Cayman  of  America;  and  even  from  the  Gavial 
of  the  Ganges.  In  the  division  of  snakes,  too,  the  Boa  of  India 
differs  from  the  nearly  allied  Python  of  America;  and  of  the 
poisonous  varieties,  the  Rattlesnake  is  peculiar  to  America,  the 
Cerastes  to  Africa,  the  Hooded  snake  to  Asia.  As  we  have  al- 
ready slated  ;  the  diversities  among  insects  are  still  more  nume- 
rous and  remarkable  than  among  the  larger  animals.  To  enter 
into  details  would  be  endless  ;  we  shall  therefore  mention  only 
one  of  the  best  known  and  widest  extended  of  all  the  insect  tribe, 
viz.  our  common  Bee.  This  insect  did  not  exist  in  America,  or 
in  New  Holland;  though  it  is  found  in  all  parts  of  the  old  world  ; 
the  wax  and  honey  of  Europe,  Asia,  and  Africa  being  obtained 
from  species  having  a  close  resemblance  to  each  other. 

Nor  are  these  differences  confined  to  land  animals  ;  the  inha- 
bitants of  the  waters  are  equally  diversified.  Thus  the  Whales  of 
the  northern  ocean  are  quite  unlike  those  of  the  south  ;  as  are  the 
Seals,  and  other  analogous  animals  in  the  polar  regions.  The 
fishes  of  different  seas,  also,  not  only  when  far  apart ;  but  even  of 
some  which  freely  communicate,  have  fish  exceedingly  dissimilar. 
Thus  the  fishes  of  the  Arabian  Gulf  are  said  to  differ  entirely 
from  those  of  the  Mediterranean  ;  notwithstanding  the  proximity 
of  these  seas.  Nor  do  these  remarks  apply  only  to  the  larger 
fish  in  these  seas,  but  hold  equally  with  respect  to  their  testace- 
ous and  molluscous  species. 

Such  are  a  few  of  the  more  striking  facts  with  regard  to  the 
distribution  of  animals  in  similar  climates  and  localities  through- 
out the  world.      We  shall  now  briefly  speak, 

2.  Of  the  Effects  of  Diversity  of  Climate  on  the  Distribu- 
tion of  Jjnimah.  In  tropical  climates,  the  qualities  of  animals, 
as  well  as  those  of  vj^ct.-^ tables,  are  developed  to  the  utmost ; 
whence  arises  that  harmonious  adaptation  of  all  the  works  of 
nature,  conspicuous,  indeed,  in  all  climates,  but  in  Tropical  cli- 
mates more  especially.  For,  where  else  than  amidst  the  profuse 
exuberance  of  the  vegetation  within  the  tropics,  could  the  Ele- 
phant^ the  Rhinoceros,  the  Giraffe,  and  other  large  quadrupeds 
find  subsistence  1  Where  else  could  we  expect  to  see  such  birds 
as  the  Ostrich  and  the  Cassowary  ?  Such  reptiles  as  the  Croco- 
dile? such  serpents  as  the  Boa?  To  what  other  part  of  the 
world  could  the  magnificent  butterflies,  the  enormous  beetles  and 


216  METEOROLOGY. 

spiders  be  so  appropriate.  Even  among  the  marine  animals  of 
Tropical  climates,  some  display  the  same  wonderful  enlargement 
of  size.  Thus  certain  species  of  the  Crab  and  Lobster^  and  va- 
rious shell-fish,  often  attain  an  enormous  magnitude.  INor  is 
there  a  developement  of  size  only,  but  of  every  other  property  in 
an  equal  degree.  Countries  within  the  tropics  exhibit  the  most 
beautiful  forms — the  most  splendid  colours  in  nature.  There,  in 
short,  is  the  most  astonishing  display  of  all  those  things  which 
seem  to  be  entirely  ornamental  :  as,  for  example,  the  singular 
plumage  of  the  Birds  of  Paradise — the  gaudy  liveries  of  many 
of  the  Parrot  tribe — the  extraordinary  and  diversified  forms  and 
colours  of  many  insects  and  shells. 

Not  only  is  there  in  Tropical  climates  an  assemblage  of  all 
the  concomitants  of  productiveness,  and  utility,  and  embellish- 
ment of  every  kind  ;  in  these  climates,  there  is  another  and  not 
less  marked  demonstration  of  the  power  and  the  wisdom  of  the 
great  Creator.  Within  the  Tropics  death,  the  last,  the  inevita- 
ble scene,  assumes  a  character  as  new  and  diversified  as  that  of 
the  life  it  terminates.  There,  rages  the  implacable  ferocity  of 
the  Tiger,  and  of  the  larger  beasts  of  prey  ;  there,  are  the  fangs 
of  the  serpent  charged  with  the  most  malignant  venom  ;  there, 
even  the  insects  are  as  formidable  as  they  are  numerous.  Nor 
is  this  intensity  of  the  destroying  power  incongruous  or  without 
an  object ;  but  obviously  is  in  perfect  harmony  \vith  the  rest  of 
creation,  and  with  the  design  of  the  Creator.  The  wonderful 
productiveness  of  animals  in  Tropical  countries  renders  unavoid- 
able some  checks  against  their  excessive  increase  :  and  in  devi- 
sing these,  the  great  Author  of  Nature  has  displayed  the  same 
attributes  that  are  manifest  in  all  his  other  works.  No  one  who 
seriously  refiects  can  doubt  either  the  wisdom  or  the  benevolence 
of  the  provision.  For  why  are  Tigers  and  Serpents  confined  to 
those  parts  of  the  world  where  their  existence  is  not  only  accor- 
dant, but  where,  for  one  great  purpose  at  least,  they  are  even 
necessary.  Surely  such  limitation  could  have  happened  only 
from  design  ;  and  the  argument  is  strengthened  a  hundred  fold  ; 
when  we  contemplate  the  striking  display  of  wisdom  and  of 
power  exemplified  in  the  singular  adaptation  of  structure  in  these 
animals,  to  tlieir  peculiar  habits.  Thus  how  wonderfully  appro- 
priate is  that  of  the  Tiger  ;  and  how  extraordinary  as  well  as 
wonderful  that  of  Serpents  !  Who  (unless  he  had  witnessed  the 
fact)  could  have  believed  that  the  animal  frame  was  capable  of 
separating  from  its  juices,  and  of  retaining  with  impunity,  a  poi- 
son instantly  fatal,  not  only  to  other  animals,  but  to  the  animal 
itself;  if  again  mingled  with  the  juices  from  which  it  had  been 
separated  ! 

Nor  in  all  these  things  is  the  benevolence  of  the  Deitv  less 


DiaTRIBUTION  OF  ANIMALS.  217 

conspicuous  than  his  wisdom.  All  must  die ;  and  death  from 
rapacious  or  venemous  animals  is  probably  not  in  any  degree 
more  pnintul  than  many  other  modes  of  death,  wliich  we  con- 
stantly witness.  There  is,  in  truth,  to  our  own  narrow  and  sel- 
fish feelings  something  exceedingly  painful  in  the  idea  of  being 
torn  to  pieces  b)'^  a  Tiger,  or  stung  to  death  by  a  Rattlesnake ; 
but  how  many  thousands  of  little  mice  are  destroyed  by  cats  ? 
and  how  many  myriads  of  unfortunate  flies  are  poisoned  by  spi- 
ders, every  day  we  live  ?  and  yet  we  hardly  commiserate  them. 
The  question,  therefore,  is  simply  a  question  of  degree  ;  and 
viewing  the  existence  and  the  destruction  of  animals,  as  they 
ought  to  be  viewed,  on  the  great  scale,  we  find  that  the  whole  is 
perfectly  in  unison.  While  in  temperate  climates  we  have  cats 
and  spiders,  designed  as  checks  on  over-productiveness  ;  amidst 
the  grandeur  and  the  luxurious  developement  of  the  Tropics,  the 
same  wise  purpose  is  executed  by  the  Tiger  and  by  the  Rattle- 
snake. 

As  wc  advance  from  the  Equator  into  the  temperate  climates, 
the  size  of  animals  in  general,  like  that  of  vegetables,  becomes 
gradually  smaller.  Like  the  vegetables,  too,  the  animals  of  tem- 
perate climates  are  more  gregarious  than  within  the  Tropics, 
Hence  number^  as  among  vegetables,  compensates  in  some  de- 
gree for  diminished  magnitude.  The  two  kingdoms  of  nature 
therefore  are  beautifully  analogous  ;  for  the  gregarious  grasses, 
which,  as  we  before  observed,  form  so  marked  a  feature  in  the 
vegetation  of  temperate  climates,  constitute  in  one  shape  or  other 
the  principal  food  of  the  gregarious  tribes  of  animals.  Thus 
the  whole  cattle  tribe — The  Ox,  the  Sheep,  the  Goat ;  the  dif- 
ferent varieties  of  Deer  ;  the  Babbit  and  Hare:  also  the  Horse 
and  the  Ass  :  with  a  multitude  of  other  well-known  animals,  of 
a  similar  character,  are  natives  chiefly  of  temperate  climates,  and 
obtain  their  nourishment  almost  entirely  from  the  grasses. 
Among  birds,  the  numerous  species  of  the  Gallinaceous,  or  Fowl 
tribe,  may  be  said  to  derive  their  food  from  the  same  source. 
Therefore,  as  regards  the  existence  of  animals,  the  gramineous 
tribe  of  plants  is  more  important  than  perhaps  any  other  ;  and 
could  not  be  annihilated,  without  the  destruction  of  the  present 
order  of  living  beings. 

As  further  examples  of  animal  species  indigenous  to  temperate 
climates,  may  be  mentioned  the  Canine  species  and  those  allied 
to  it,  most  of  which  are  more  or  less  carnivorous ;  also  the  Hogy 
and  a  variety  of  other  animals  that  need  not  be  here  enume- 
rated. The  Hog  tribe,  as  is  well  known,  are  omniverous  ;  but  in 
their  natural  state,  they  feed  principally  on  the  seeds  and  roots  of 
plants.  Among  birds  peculiar  to  temperate  climates  are  various 
tribes  of  Water-foud  that  subsist  on  fish  and  on  insects.  Of  the 
^  19 


218  METEOROLOGY. 

smaller  land  birds,  the  various  So7igsfe)'S  offer  a  remarkable  con- 
trast to  those  of  similar  form  within  the  Tropics;  not  only  from 
their  more  melodious  notes,  but  from  the  simple  colouring  of 
their  feathers.  In  temperate  countries  the  Insects  are  still  exceed- 
ingly multiplied  ;  though,  in  general,  like  the  other  animals,  they 
are  much  smaller  in  size  than  those  within  the  Tropics  ;  their 
forms,  their  colours,  and  other  peculiarities  also  are  much  less 
remarkable. 

As  we  advance  toward  the  Poles,  the  animals  of  temperate 
climates  are  observed  gradually  to  decline  in  number.  The  ve- 
getable feeders  bec(mie  reduced  to  a  few  hardy  species  ;  and 
at  length  in  the  remote  north  and  south  scarcely  any  vegetable 
feeders  remain.  So  far  as  shrubby  plants  continue  to  grow  in 
these  inhospitable  regions,  individuals  of  the  Squirrel  tribe  find 
subsistence  on  their  seeds  and  roots.  But  the  most  remarkable 
herbivorous  animal  is  i\\e  Reindeer ;  whose  principal  food  is 
afforded  by  nature  in  a  species  of  moss  peculiar  to  very  cold  cli- 
mates. Those  that  exist  beyond,  are  either  carniverous  or  pisci- 
vorous. The  Arctic  Fox  and  the  Bear  are  familiar  instances, 
as  terminating  the  Zoological  series,  viewed  in  connection  with 
the  influence  of  climate. 

We  have,  in  the  last  place,  to  notice  what  is  most  remarkable 
in  the  distribution  of  Marine  animals. 

For  the  reasons  before  stated,  the  general  temperature  of  the 
ocean  ditfers  considerably  from  that  of  the  land.  Owing  to  this 
difference  of  temperature,  and  to  the  peculiar  mode  of  subsistence 
of  marine  animals,  which  find  their  prey  chiefly  in  the  waters  they 
inhabit;  the  distribution  of  these  animals  varies  much,  as  compared 
with  the  distribution  of  animals  that  are  entirely  terrestrial ;  parti- 
cularly within  the  frigid  zone.  It  is  true,  indeed,  that  in  all  cli- 
mates, the  denizens  of  peculiar  localities,  as  fresh  water  species 
and  those  that  resort  to  the  shallows  on  the  coast,  are  influenced 
by  the  climate  nearly  as  much  as  land  animals:  and  within  the 
Tropics,  this  influence  extends  in  some  degree  even  to  the  species 
that  dwell  on  the  wide  ocean.  But  far  to  the  north,  and  to  the 
south,  such  species  are  influenced  in  a  manner  altogether  differ- 
ent. Thus  the  largest  of  known  animals,  the  Whale,  and  of  course 
those  other  animals  that  become  its  prey,  roam  through  the  ut- 
most Polar  seas  ;  where  on  land  the  intensity  of  the  cold  would 
prevent  the  existence  of  any  animal  whatever.  In  that  climate 
t!ie  whale  is  enabled  to  live,  solely  on  accountof  the  greater  warmth 
of  the  Polar  ocean,  as  has  been  formerly  explained.  Among  the 
larger  inhabitants  of  the  ocean  in  Tropical  climates,  may  be  men- 
tioned the  Shark  tribe  ;  which  in  respect  of  ferocity  and  voraci- 
ousness, may  be  clashed  with  the  tiger,  or  any  kindred  species  on 
land.  'J'he  influence  of  climate  on  marine  animals  is  further  shown. 


DISTRIBUTION  OF  ANIMALS.  219 

as  we  have  said,  by  the  enormous  size  of  many  of  the  Tropical 
shell-fish  and  mollusca.  The  colouring  of  these  and  also  of  other 
productions  of  the  Equatorial  seas,  often  exliibits  so  much  lustre 
and  beauty,  as  to  rival  the  most  splendid  of  the  feathered  race.  In 
temperate  climates,  and  from  the  equal  temperature  of  the  sea, 
even  within  the  frigid  zone;  it  is  remarkable  that  fish,  like  terres- 
trial animals,  are  much  disposed  to  be  gregarious.  The  shoals  of 
Herring,  MackareU  and  other  well  known  visitants  of  our  coast, 
are  familiar  examples  of  the  gregarious  tendency.  The  Salmon 
and  the  Sturgeon  may  be  adduced  as  instances  of  fish  inhabiting 
chiefly  the  rivers  of  the  temperate  and  colder  countries.  While 
in  the  same  climates,  instead  of  the  magnificent  Pearl  oyster  of 
the  Tropics,  there  appears  our  common  Oyster,  so  diminutive  and 
unsightly,  yet  so  profitable  to  man. 

We  have  thus  seen  that  animals,  like  plants,  have  in  general 
been  adapted  to  particular  climates.  The  numerous  cold-blooded 
animals  of  the  Tropics — even  the  warm-blooded  Tiger  itself,  amid 
the  Polar  snows  would  instantly  perish.  The  Arctic  bear  would 
be  not  less  unable  to  live,  under  the  scorching  rays  of  a  vertical 
sun.  Yet  though  adaptation  to  one  climate  be  the  general  law 
regarding  animals  as  well  as  plants  ;  some  species  of  animals  have 
as  remarkably  as  some  species  of  plants,  the  faculty  of  accommo- 
dating themselves  to  all  climates.  These  species,  like  the  plants 
similarly  endowed,  are  for  the  most  part  natives  of  temperate  cli- 
mates;  the  transition  from  such  climates  to  either  extreme,  being 
much  less  violent  than  from  one  extreme  to  the  other.  Thus  our 
domestic  animals,  that  have  been  successively  introduced  into  the 
New  World  at  various  periods  since  its  discovery,  are  now,  in  in- 
credible numbers,  spread  over  the  whole  of  that  vast  continent, 
from  Canada  to  Paraguay.  The  greatest  increase  has  been  of  the 
Horse,  the  Ox,  the  Sheep,  the  Goat,  the  Dog,  the  Cat,  and  the 
Hog.  The  Rat,  too,  though  an  unwelcome  intruder,  has  been  not 
the  least  prolific.  The  different  varieties  of  domestic  Poultry  have 
multiplied  to  an  equal  extent.  Even  insects  have  been  introduced, 
and  spread  in  like  manner,  as  is  well  known  to  horticulturists. 

Like  plants,  most  animals  also  are  readily  domesticated,  and 
thrive  in  climates  similar  to  those  of  which  they  are  natives.  The 
most  striking  instance  is  the  Rein-deer ;  so  lately  as  in  the  year 
1773  introduced  into  Iceland,  and  now  exceedingly  numerous  in 
the  interior  of  that  country.  From  these  powers  of  accommodation 
to  climate,  from  the  agency  of  man,  and  from  accidental  causes  ; 
the  distribution  of  the  larger  animals  over  the  globe  has,  in  com- 
paratively recent  times,  been  very  much  modified.  Nor  is  there 
any  reason  to  believe  that  the  distribution  of  these  animals  is  yet 
stationary;  but,  on  the  contrary,  that  their  distribution  will  under- 
go still  further  changes. 


220  METEOROLOGY. 

Amonir  the  more  remarkable  habits  of  animals,  may  be  noticed 
the  migratory  propensities  of  certain  species.  The  migration  of 
land  animals  is,  of  course,  always  much  limited,  and  may  be  en- 
tirely prevented  by  natural  obstacles — the  asperities  of  the  earth's 
surface — sands — deep  rivers — or  other  large  accumulations  of 
water.  But  many  birds  and  even  insects,  possessing  powerful 
locomotion,  and  whose  course  is  through  the  air,  may  literally  be 
said  to  follow  the  sun  in  their  migratory  progress.  It  is  hardly 
necessary  to  state,  as  examples,  the  birds  of  passage,  so  well 
known  as  the  Swallo\v  and  the  Cuckoo.  These  birds  during  the 
summer  months  visit  our  northern  climate,  and  feed  on  insects, 
whose  multiplication  would  otherwise  be  boundless.  Having  ful- 
filled their  office  here  ;  on  the  declination  of  the  sun,  they  again 
retire  to  the  south  ;  and  are  succeeded  by  different  birds  from  coun- 
tries still  further  north.  Such  are  the  Woodcock  and  others,  which 
escape  to  our  shores  from  the  rigorous  cold  of  a  Polar  winter. 
Nor  is  migration  confined  to  the  higher  classes  of  animals.  The 
wonderful  powers  of  flight  possessed  by  many  insects,  enable 
them  to  travel  over  an  immense  extent  of  country.  The  Locust 
and  the  Ant  tribe  are  familiar  examples.  These  insects  occasion- 
ally migrate  in  coundess  swarms  from  the  lands  to  which  they 
are  indigenous,  and  lay  waste  others  far  remote. 

Equally  remarkable  is  that  habit  of  animals  termed  Hybernation. 
Like  the  plants  of  temperate  climates,  some  animals  have  the  fa- 
culty of  passing  the  colder  season  of  the  year  in  a  state  of  sleep. 
The  Hedgehog  and  the  Dormouse  may  be  mentioned  as  examples 
of  quadrupeds  possessing  this  faculty.  Additional  instances  might 
be  given  in  all  the  classes  of  animals.  Nearly  allied  to  Hyberna- 
tion, is  that  remarkable  instinct  which  guides  many  of  the  inferior 
animals  to  deposit  their  eggs  in  the  earth,  or  in  some  other  place 
of  safety  ;  that  they  may  be  preserved  during  the  season  of  dimi- 
nished temperature.  This  instinct  is  particularly  observable  in 
insects  whose  lives  are  ephemeral,  or  are,  at  the  utmost,  prolonged 
for  a  summer. 

There  is  yet  another  circumstance  that  remains  to  be  noticed, 
as  being  connected  with  the  adaptation  of  animals  to  the  climates 
in  which  they  live  ;  namely,  the  Clothing  or  covering  with  which 
tliey  have  been  supplied  by  nature.  Every  one  is  acquainted  with 
the  general  fact,  that  wool,  fur,  eider-down,  and  similar  articles, 
are  obtained  for  the  most  part,  not  from  the  copious  source  of 
every  superfluous  production,  the  countries  within  the  tropics,  but 
from  the  cold,  and  comparatively  unprolific  regions  of  the  tempe- 
rate and  of  the  frozen  zones  ;  where  they  have  constituted  the 
appropriate  vesture  of  different  animals.  Perhaps,  in  the  whole 
range  of  creation  there  is  not  anything  more  calculated  to  excite 
our  admiration.     However  we  may  view  these  means  of  guard- 


DISTRIBUTION  OF  ANIMALS.  221 

ing  animals  from  being  injured  by  the  cold  ;  whether  as  a  part 
of  that  conservative  faculty  with  which  animals  have  been  en- 
dowed, and  by  wliich  their  existence  is  maintained ;  or  as  an  im- 
mediate act  of  Providence;  still  the  adaptations  are  so  striking  and 
obvious,  as  to  render  it  impossible  to  doubt  for  a  moment,  that 
they  have  all  been  contrived  for  the  purpose  which  is  accom- 
plished;  and  that  they  are  the  results  of  foreknowledge  and  of 
design. 

We  have  thus  given  a  rapid  sketch  of  the  distribution  of  ani- 
mals over  the  globe.  In  this  sketch  we  have  endeavoured  to  point 
out  the  wonderful  adaptations  of  the  several  classes  of  animals  to 
the  circumstances  in  which  they  are  placed  ;  together  with  the 
beautiful  symmetry  and  equilibrium  exhibited  in  zoology,  not  less 
than  in  the  arrancrements  of  inanimate  matter.  Throuf^hout  we 
have  intentionally,  and  as  far  as  was  possible,  avoided  those  de- 
tails, the  consideration  of  which  belongs  to  other  departments. 
But  it  has  been  our  aim  to  state  such  prominent  facts,  as  appeared 
best  calculated  for  the  elucidation  of  our  argument.  In  particular, 
it  has  been  our  desire  to  show — how  number  amonff  the  weak  is 
made  to  compensate  for  magnitude  among  the  strong;  how  exube- 
rance in  one  species  is  made  to  contribute  to  the  existence  of  an- 
other ;  how  ornament  and  boundless  profusion  characterize  the 
countries  within  the  tropics,  while  the  temperate  climates  are  not 
less  distinguished  by  utility  and  capacity  for  change  ;  how,  even 
in  the  rigorous  and  barren  neighbourhood  of  the  Poles,  where  life 
becomes  a  struggle  for  existence,  animals  have  been  expressly 
furnished  with  clothing  appropriate  to  these  regions ; — in  short, 
we  have  endeavoured  to  demonstrate,  how  every  animal,  in  every 
climate,  has  its  day  ;  and  by  some  peculiar  contrivance,  has  been 
enabled  to  maintain  its  rank  in  creation,  and  to  assist  in  preserving 
the  general  equilibrium. 

Hitherto  we  have  considered  the  works  of  nature  without 
reference  to  Man.  For  aught  we  can  see  to  the  contrary,  they 
might  all  have  existed,  and  every  arrangement  and  operation 
might  have  been  very  nearly,  if  not  exactly,  the  same  as  at  pre- 
sent; though  man  had  never  been  called  into  being.  Butstill,  for 
a  moment  longer,  keeping  man's  existence  out  of  view  ;  let  us,  as 
under  a  former  division  of  this  Treatise,  inquire,  vv'hat  would 
have  been  the  r^se  of  all  this  elaborate  design,  without  an  ulterior 
object.  Would  an  intelligent  Creator  have  made  such  a  world, 
and  have  left  it  thus  incomplete  ?  It  is  evident  that  the  other 
beings  inhabiting  this  earth,  live  and  die,  without  in  the  slightest 
degree  comprehending  the  vast  system  of  which  they  constitute  a 
part.  Hence  they  are  merely  unconscious  agents,  from  which 
their  Maker,  while  he  has  furnished  them  with  the  instincts  ne- 
cessary to  their  existence,  and  has  awarded  equal  justice  to  all, 

19  - 


I 


222  METEOROLOGY. 

has  yet  chosen  to  withhold  the  privilege  of  reason.  That  a  Crea- 
tor, evidently  as  benevolent  as  he  is  wise,  might,  for  his  own 
gratification,  have  made  such  a  world,  and  without  any  other 
inhabitants,  is  indeed  possible.  But,  even  admitting  that  possi- 
bility, the  probability  surely  is,  that  he  would  not  there  have 
finally  "rested  from  his  labour."  His  benevolence  would  have 
prompted  him  to  communicate  to  other  beings  a  portion  of  the 
gratification,  which  he  himself  is  supposed  to  derive  from  the 
contemplation  of  his  works.  In  the  beautiful  world  which  he 
had  created,  he  would  have  wished  to  see  one  being  at  least,  capa- 
ble of  appreciating  to  a  certain  extent  his  design  and  his  objects. 
Such  is  a  plain  inlerence  deducible  from  the  manifest  attributes  of 
the  Creator  ;  and  what  is  the  fact?  Is  not  man  such  a  being  as 
we  have  supposed  ?  Throughout  the  world,  though  perfectly 
independent  of  him,;^is  there  not  a  clear  foretoken  of  his  existence  ? 
Has  he  not  been  placed  at  the  head  of  that  world,  so  obviously 
prepared  for  him,  and  thus  constituted  "  the  Minister  and  Inter- 
preter of  nature  ?"  Surely  no  one  will  be  inclined  to  doubt  that 
such  is  the  situation  of  man  in  the  world.  Equally  undeniable, 
is  the  striking  accordance  of  these  deductions  from  the  view  of 
external  objects,  with  what  is  written  of  the  origin  of  man  by  the 
sacred  historian  :  "  and  God  said,  that  it  (the  world  which  he  had 
prepared)  was  good.  And  God  said,  Let  us  make  man  in  our  own 
image,  after  our  own  likeness,  (that  is  to  say,  endowed  with 
reason  and  with  the  power  of  reflection).  And  let  him  have 
dominion  over  the  fish  of  the  sea,  and  over  the  fowl  of  the  air, 
and  over  the  cattle,  and  over  every  creeping  thing,  that  creepeth 
on  the  earth." 

We  thus  arrive  at  another,  and  to  us  the  final  step  in  the  great 
design  of  the  Omnipotent:   the  creation  and  the  faculties  of  Man. 


Section  III. 
Of  the  present  Position  and  future  Prospects  of  Man, 

The  consideration  of  the  faculties  of  man,  and  of  his  position 
in  the  world  he  inhabits,  belongs,  in  all  its  details,  to  another 
department.  We  advert  to  these  subjects  here,  with  the  view 
only  of  completing  our  sketch  of  the  physical  relations  of  animated 
beings.  'J'lic  observations  we  have  to  ofler  will  be  comprised 
under  two  heads: — as  to  the  means,  by  which  man  has  acquired 
and  maintains  the  ascendency  .,he  enjoys  : — as  to  the  conclusions 
to  be  drawn,  from  man's  elevated  position,  and  from  his  superior 
intellectual  character. 

With  regard  to  the  means  by  which  man   has   acquired  and 


POSITION  AND  PROSPECTS  OF  MAN.  223 

maintains  his  ascendency,  it  may  be  observed,  that  these  means 
are  quite  peculiar  ;  and  iar  from  being  such,  as  at  first,  perhaps, 
we  might  deem  conducive  to  such  an  object :  though  when  once 
known  and  understood,  the  beautiful  design  and  harmony  they 
evince,  immediately  become  apparent. 

The  supremacy  of  man  has  notheen  the  result  of  his  own  per- 
sonal strength,  nor  is  it  so  upheld.  On  the  contrary,  many  ani- 
mals are  larger  and  more  powerful  than  he  is  ;  while  few  of  his 
size,  are  naturally  so  incapable  of  self-defence  ;  or  during  so  long 
a  period  suffer  from  the  dependent  helplessness  of  infancy  and  of 
old  age.  Neither  is  his  frame  superior  in  external  adaptation  to 
climate  :  for  while  nature  has  furnished  other  animals  with 
clothing  appropriate  to  the  temperature  in  which  they  live,  man 
has  been  brought  into  being  absolutely  naked  ;  and  moreover  re- 
mains so,  in  every  climate  he  inhabits,  from  the  Equator  to  the 
Poles.  Lastly,  the  pre-eminence  of  man  has  not  been  owing  to  his 
more  extensive  range  of  diet;  or  to  his  greater  ability  for  assimi- 
lation :  for  though  man  be  omnivorous  in  one  sense  of  the  term, 
he  is  not  omnivorous  according  to  the  application  of  the  term  to 
other  animals;  that  is  to  say,  man  does  not  eat  indiscriminately 
of  every  kind  of  aliment,  in  the  state  in  which  it  is  afforded  by 
nature  ;  for  even  in  his  rudest  condition,  he  adopts  some  process 
of  cookery.  How  then  has  man  gained  the  high  station  which 
he  occupies  ?  The  answer  is  simply — by  his  Reason.  Man 
has  been  created  a  reasonable  being;  and  this  endowment  amply 
compensates  to  him  for  the  want  of  the  animal  requisites  of 
strength — for  deficiency  of  natural  covering — and  for  his  restrict- 
ed ability  in  assimilating  his  food.  By  his  reason  he  is  enabled  to 
command  the  strength  of  the  elephant ;  to  choose  from  every 
production  of  nature  whatever  is  adapted  for  his  clothing,  and 
thus  to  array  himself  according  to  his  pleasure,  or  the  exigencies 
of  the  climate  in  which  he  resides  ;  to  extract  wholesome  nou- 
rishment from  the  most  unpromising,  even  from  the  most  delete- 
rious articles.  There  was  no  necessity,  therefore,  why  man 
should  himself  be  as  unwieldy  as  an  elephant;  or  be  encumbered 
with  any  vesture  that  in  some  situations  might  be  oppressive  ;  or 
be  able  to  digest,  without  culinary  preparation,  any  coarse  and 
intractable  substances.  Thus,  mere  animal  endowments  not 
being  requisite,  the  Creator's  wisdom  has  been  displayed  in  an- 
other manner,  and  with  a  wider  scope.  In  furtherance  of  his 
design.  He  has  limited  the  bulk  of  the  human  species  to  that 
happy  medium,  combining  strength  with  convenience;  and  to  an 
organization  delicate  and  sensitive  in  the  highest  degree,  but 
nevertheless  accommodating.  He  has  superadded  a  form  at  once 
peculiar,  appropriate,  and  beautiful ! 

When  speaking  of  temperate  climates,  we  remarked,  that  they 


224  METEOROLOGY. 

seemed  to  be  characterized  by  the  utility  of  their  productions  ; 
and  that  the  plants  and  animals  of  these  climates,  generally  pos- 
sessed oreater  powers  of  accommodation  than  those  of  either  of 
the  extreme  climates.  Now  Man,  by  an  express  arrangement  of 
his  Maker,  has  apparently  been  constituted  a  native  of  temperate 
qlimates;  and  only  in  these  climates  can  his  powers  be  said  to  be 
completely  deveh)ped.  Within  the  tropics,  indeed,  human  ex- 
istence is  nourishing;  for  there  the  immediate  bounty  of  Provi- 
dence affords  to  man  a  copious  and  admirably  adapted  nutriment. 
Yet  in  the  midst  of  that  profusion,  and  without  any  adequate 
motive  to  call  forth  exertion,  his  reason  too  often  languishes  ;  while 
his  animal  tendencies  predominate  ;  and  his  life  is  spent  in  apathy 
and  in  sensual  gratifications.  On  the  other  hand,  under  the 
cheerless  sky  of  the  frigid  zone,  imperfectly  nourished  by  scanty 
and  unsuitable  food,  the  powers  of  his  mind,  like  those  of  his 
body,  are  stunted  ;  or  are  engaged  solely  in  combating  the  ri- 
gours of  his  situation.  But  in  the  temperate  climates  the  evil 
consequences  of  both  these  extremes  are  avoided,  while  the  bene- 
ficial influences  of  climate  remain.  Urged  by  the  stimulus  of 
necessity,  and  at  the  same  time  having  at  his  command  the 
astonishing  capability  of  nature,  man  is,  in  temperate  climates, 
surrounded  by  motives  of  every  kind,  and  his  faculties  thus  attain 
their  utmost  developement.  As  familiar  examples  of  the  effect 
of  this  expansion  of  the  human  reason,  let  us  view  man  under 
the  three  aspects  to  which  we  have  before  alluded  ;  namely,  with 
reference  to  his  strength,  his  food,  and  Wis  clothing,  inclusive  of 
his  habitation. 

In  the  first  place,  with  regard  to  his  strength.  The  strength 
of  man  is  not  only  that  which  is  his  own,  almost  infinitely  mag- 
nified by  ingenious  mechanical  devices  of  every  kind,  and  of 
every  degree,  up  to  the  stupendous  agency  of  steam  ;  man  has, 
moreover,  subdued  to  his  service  many  of  the  larger  animals, 
"while  those  whi(^li  he  cannot  so  appropriate,  he  destroys.  As 
weapons,  he  wields  every  instrument  offensive  and  defensive, 
from  the  rude  but  effective  club  or  arrow,  to  the  warlike  engines 
to  which  he  has  applied  the  discovery  of  gunpowder.  Whatever 
his  wants  require,  he  obtains  by  tools  ;  from  the  humble  spade, 
to  that  perfection  of  machinery,  which  almost  rivals  the  opera- 
tions of  intelligence  itself.  In  the  next  place,  view  man  with 
reference  to  his  food  :  what  wonders  has  not  his  reason  enabled 
him  to  achieve  among  the  fellow  inhabitants  of  his  own  tempe- 
rate climate.  In  the  vegetable  kingdom,  let  us  consider  the  as- 
tonishing mutations  and  increase  of  the  cerea/ia,  or  corn  tribes  ; 
tlie  transfornuUion  of  the  sour  and  forbidding  Crab  into  the  rich 
and  fragrant  Aj)ple;  of  the  harsh  and  astringent  Sloe  ijito  the  de- 
licious Plum  ;  of  the  coarse  and  bitter  sea-side  Brassica  into  the 


POSITION  AND  PROSPECTS  OF  MAN.  225 

nutritious  and  grateful  Cauliflower:  all  which  changes,  and  nu- 
merous others  of  a  like  kind,  have  been  efl^ectcd  by  man.  Nor 
have  the  transformations  which  he  has  produced  among  animals 
been  less  wonderful  than  those  among  vegetables.  All  the  nu- 
merous varieties  of  cattle,  of  sheep,  of  horses,  of  dogs,  of  poultry, 
and  of  all  the  other  animals  reared  as  food,  or  for  any  purpose 
domesticated,  have  sprung  from  a  few  wild  and  unattractive  spe- 
cies ;  and  have  been  made  what  they  are,  in  a  great  degree,  by 
his  intervention.  Moreover,  the  most  useful  of  these  varieties  of 
animals  have  been  transported  by  man  into  every  region  of  the 
globe,  to  which  he  has  himself  been  able  to  penetrate.  Lastly, 
in  the  clothing  and  habitations  of  man,  the  surpassing  influence 
of  his  reason  is  equally  conspicuous.  For  covering  his  naked 
body,  a  surface  of  considerable  extent  is  necessary  ;  larger,  in- 
deed, than  is  presented  by  any  natural  texture,  unless,  perhaps, 
by  the  skins  of  other  animals,  or  by  the  leaves  of  some  plants  ; 
which  therefore,  in  the  rudest  states  of  society,  usually  consti- 
tute his  only  dress.  But  by  the  art  of  weaving^  he  has  been 
enabled  to  produce  garments  of  any  size,  and  from  materials  that 
would  seem  the  least  fitted  for  such  conversion.  Thus  man  can 
not  only  clothe  himself  in  any  manner,  and  according  to  the  tem- 
perature of  the  climate  in  which  he  lives  ;  but  he  can  associate 
with  the  articles  of  his  dress  every  species  of  ornament  which 
his  fancy  may  dictate.  His  choice  of  materials  for  the  construc- 
tion of  dwellings  is  not  less  extensive  than  that  of  his  clothing. 
As  climate  and  other  circumstances  may  require,  he  abides  in  the 
humble  cabin,  or  in  the  splendid  palace  ;  in  the  temporary  hut, 
or  in  the  enduring  castle,  formed  to  withstand  alike  the  tempest 
of  war,  and  of  the  elements. 

Such  is  man,  and  such  are  a  few  of  tliose  great  changes  in  this 
world,  which,  under  the  guidance  of  his  reason,  he  has  had  the 
power  to  accomplish.  And  what  a  splendid  evidence  of  design 
and  of  preconcerted  arrangement  on  the  part  of  the  great  Creator 
is  thus  exhibited,  by  viewing  the  inherent  properties  of  matter, 
and  its  various  conditions,  witii  reference  to  the  works  of  man. 
Had  water,  for  instance,  not  been  constituted  as  it  is,  man  could 
never  have  formed  the  steam  engine.  Had  not  the  productions 
of  the  temperate  climates  been  formed  Nvith  that  capability  for 
change,  by  which  they  are  so  much  distinguished,  man  could 
never  have  so  moulded  them  to  his  uses,  by  altering  their  cha- 
racter. There  was  no  reason  why  such  properties  should  have 
been  communicated  ;  there  was  even  no  reason  why  the  objects 
in  w^hich  these  properties  exist,  should  have  been  created.  But 
they  have  been  so  created  ;  and  what  are  we  to  infer?  No  one 
surely  will  contend  that  they  have  been  the  result  of  chance,  or 


226  METEOROLOGY. 

have  been  created  without  an  object.  They  must  therefore  have 
been  created  with  design  ;  and  if  with  design — most  obviously 
with  design  having  reference  to  the  being  man,  not  yet  in  ex- 
istence. 

Thus  far  we  have  considered  the  state  at  which  the  earth  has 
arrived,  and  man,  an  animal  endowed  with  reason,  placed  as  its 
chief  inhabitant.  But  we  may  yet  extend  our  view  to  the  pros- 
pects in  futurili/. 

We  have  seen  that  this  earth  has  not  suddenly  emerged  from 
chaos  to  its  present  condition  ;  but  that  by  a  succession  of  violent 
and  disruptive  changes,  it  has  been  progressively  brought  into 
different  conditions,  and  progressively  tenanted  by  higher  orders 
of  beings.  We,  the  last  of  the  series,  in  our  owni  creation  and  in 
the  faculties  with  which  we  have  been  endowed,  behold  the  most 
striking  exemplification  of  the  wisdom,  and  of  the  power  of  the 
Deity.  But  does  the  great  design  abruptly  terminate  here?  Has 
this  earth  arrived  at  the  ultimate  stage  of  its  existence  ?  Have 
its  inhabitants  attained  the  utmost  perfection  of  which  they  are 
capable  ?  Are  there  not  further  convulsions,  and  still  higher 
orders  of  beings  in  contemplation  ?  Tlie  answers  to  these  ques- 
tions are  known  only  to  the  great  Author  of  the  universe,  and 
concern  us  not.  There  is  one  question,  however,  connected  with 
this  siibject,  in  which  we  are  deeply  and  personally  interested — 
What  is  to  become  of  man?  Is  the  being  who,  surveying  na- 
ture, recognizes  to  a  certain  extent,  the  great  scheme  of  the  uni- 
verse ;  but  who  sees  infinitely  more  which  he  does  7iot  compre- 
hend, and  which  he  ardently  desires  to  know  ; — is  he  to  perish 
like  a  mere  brute — nil  his  knowledge  useless  ;  all  his  most  earn- 
est wishes  ungratified  ?  How  are  we  to  reconcile  such  a  fate 
with  the  wisdom — the  goodness, — the  impartiil  justice — so 
strikingly  displayed  throughout  the  world  by  its  Creator?  Is  it 
consistent  with  any  one  of  these  attributes,  thus  to  raise  hopes  in 
a  dependent  being,  which  are  never  to  be  realized  ?  thus  to  lift, 
as  it  were,  a  corner  of  the  veil — to  show  this  being  a  glimpse  of 
the  splendour  beyond — and  after  all  to  annihilate  him  ?  With 
the  character  and  attributes  of  the  benevolent  Author  of  the  uni- 
verse, as  deduced  from  His  works,  such  conceptions  are  abso- 
lutely incompatible.  The  question  then  recurs — What  is  to  be- 
come of  man  ?  That  he  is  mortal,  like  his  fellow  creatures,  sad 
experience  teaches  him;  but  does  he,  like  them,  die  entirely? 
Is  there  no  part  of  him,  that,  surviving  the  general  wreck,  is  re- 
served for  a  higher  destiny  ?  Can  that,  within  man,  which  rea- 
sons like  his  immortal  Creator — which  sees  and  acknowledges 
His  wisdom,  -.ind  approves  of  His  designs,  be  mortal  like  the 
rest?     Is  it  probable,  nay,  is  it  possible,  that  what  can  thus  com- 


POSITION  AND  PROSPECTS  OF  MAN.  227 

prebend  the  operations  of  an  immortal  Agent,  Is  not  itself  im- 
mortal? 

Thus  has  reasoned  man  in  all  ages  ;  and  his  desires  and  his 
feelings,  his  hopes  and  his  fears,  have  all  conspired  with  his  rea- 
son, to  strengthen  the  conviction,  that  there  is  something  within 
him  which  cannot  die.  That  he  is  destined,  in  short,  for  a  future 
state  of  existence,  where  his  nature  will  be  exahed,  and  his  know- 
ledge perfected  ;  and  where  the  great  design  of  his  Creator, 
commenced  and  left  imperfect  here  below,  will  be  completed. 


BOOK    III. 

OF  THE  CHEMISTRY  OF  ORGANIZATION  :  PARTICULARLY  OF  THE  CHEMICAL 
PROCESS  OF  digestion;  AND  OF  THE  SUBSEQUENT  PROCESS  BY  WHICH 
VARIOUS  ALnrENTARY  SUBSTANCES  ARE  ASSIMILATED  TO,  AND  BECOME 
COMPONENT  PARTS  OF,  A  LIVING  BODY. 

Having  in  the  foregoing-  pages,  given  a  summary  view  of  the 
Chemical  properties  of  bodies  not  organized,  and  of  the  laws  of 
their  union  ;  having  also  considered  the  general  relations  of  ina- 
nimate matter  and  of  organized  beings,  on  the  great  scale  in  which 
they  are  offered  to  us  by  nature,  together  with  the  present  posi- 
tion and  future  prospects  of  man  ;  we  now  proceed,  in  the  last 
place,  to  inquire  n)ore  particularly  into  the  means  by  which  or- 
ganization is  accomplished  ;  or,  in  other  words,  to  give  a  sum- 
mary view  of  those  chemical  properties,  and  laws  of  union,  by 
whicii  organized  beings  are  distinguished  from  inorganic  matters. 


CHAPTER  I. 

OF  THE  NATURE  AND  COMPOSITION  OF  ORGANIZED    BODIES  IN  GENERAL,  AS 
COMPARED  WITH  INORGANIC  MATTERS. 

**  A  LIVING  being  considered  as  an  object  of  chemical  research, 
is  a  laboratory,  within  which  a  number  of  chemical  operations 
are  conducted  ;  of  these  operations,  one  chief  object  is  to  produce 
all  those  phenomena,  which  taken  collectively  are  denominated 
/>//e  ;  while  another  chief  object  is  to  devclope  gradually  the 
corporeal  machine  or  Laboratory  itself,  from  its  existence  in  the 
condition  of  an  atom,  as  it  were,  to  its  utmost  state  of  perfection. 
From  this  point  of  utmost  perfection,  the  whole  begins  to  decline 
as  gradually  as  it  had  been  developed  ;  the  operations  are  per- 
formed in  a  manner  less  and  less  perfect,  till  at  length  the  being 
ceases  to  live  ;  and  the  elements  of  which  it  is  composed,  again 
set  free,  obey  the  general  laws  of  inorganic  nature."* 

Such  is  the  history  of  organic  existence  ;  nor,  though  the  pe- 
riods of  developement  and  of  decay  be  infinitely  varied  in  dif- 
ferent species,  does  a  single  individual  remain  for  a  moment  sta- 
tionary ;  but  all,  sooner  or  later,  transcend  their  prime,  and  finally 
share  the  common  lot  of  dissolution. 

That  peculiar  principle  or  principles,  which  under  some  con- 
dition or  oilier,  exists  in  all  organized  beings,  and  by  wliich  they 

•  rJerzclius,  Traitc  de  Chimic,  torn.  v.  p.  1. 


COMPOSITION  OF  ORGANIZED  BODIES.  229 

are  distinguished  from  inanimate  matter,  has  received  various  ap- 
pellations. In  the  present  inquiry  these  principles  may  be 
viewed  as  agents  :  and  to  discriminate  them  from  Heat,  Electri- 
city, and  other  agents  or  inorganic  matters,  they  may  be  denomi- 
nated organic  agents.  In  conducting  our  investigations  into  the 
nature  of  these  principles  or  agents,  our  difficulty  will  be  much 
lessened,  by  endeavouring  previously  to  have  a  clear  understand- 
ing of  what  these  agents  actually  do.  We  shall,  therefore,  in 
the  first  place,  give  a  short  sketch, 

1.  Of  Organic  Bodies  considered  as  Chemical  Compounds. 
— In  their  well-marked  forms  no  two  things  perhaps  can  be  con- 
ceived to  offer  a  stronger  contrast,  than  the  two  great  divisions  of 
organic  bodies — vegetables  and  animals.  Yet  these  two  kinds  of 
bodies  so  gradually  approximate,  and  seem  even  to  coalesce,  thai  it 
is  not  possible  to  say  where  the  one  ends  and  the  other  begins. 
The  same  remark  applies  to  the  chemical  composition  of  vegeta- 
bles and  animals.  Vegetable  substances,  in  general,  contain 
essentially  no  more  than  three  elements.  Hydrogen,  Carhon,  and 
Oxygen;  while  animal  substances  usually  involve  a  fourth,  Azote. 
Yet  there  are  many  vegetable  substances,  of  whose  composition, 
azote  forms  a  considerable  part;  while  certain  animal  substances 
are  entirely  wanting  in  that  principle.  It  is  obvious,  therefore, 
that  the  mere  chemical  composition  of  a  substance,  at  least  its 
essentially  consisting  of  three  or  four  of  these  elements,  will  not 
enable  us  to  determine  whether  it  be  vegetable  or  animal ;  and 
that,  in  many  substances,  when  this  point  happens  to  be  doubtful 
or  unknown,  we  must  have  other  data  before  we  can  form  a  con- 
clusion. Besides  these  four  elements,  of  which  all  organic  sub- 
stances are  essentially  compounds  ;  other  principles  generally 
enter  into  their  composition.  These  other  principles  are  in  very 
minute  quantity,  and  are  not  so  essential  to  the  actual  existence 
of  organic  substances,  as  the  four  constituent  elements  above 
named;  yet,  however  minute  the  quantity,  the  influence  of  these 
other  principles  seems  to  be  most  important ;  they  are.  Sulphur, 
Phosphorus,  Chlorine,  Fluorine,  Iron,  Potassium,  Sodium,  Cal- 
cium, Magnesium,  and  probably  more  besides.  These  princi- 
ples, have,  by  most  chemists,  been  deemed  extraneous,  or  foreign 
to  organized  bodies  ;  but  we  shall  presently  show,  that  there 
is  good  reason  to  believe,  that  the  office  of  such  additional  prin- 
ciples, though  difl'erent  from  that  of  the  constituent  elements, 
is  nevertheless  most  remarkable.  These  four  elements,  along 
with  the  additional  principles,  are,  in  the  present  state  of  our  know- 
ledge, alike  denominated,  The  Ultimate  Elements  of  organized 
bodies  ;  but  hydrogen,  carbon,  oxygen,  and  azote,  may  be  termed, 
for  sake  of  distinction,  the  essential  elements ;  and  sulphur,  phos- 
phorus, &c.  the  incidental  elements  of  such  bodies.     The  com- 

20 


230  CHEMISTRY  OF  ORGANIZATION". 

binations  of  these  ultimate  elements  with  one  another,  according 
to  certain  laws,  produce  what  are  denominated  the  Immediate,  or 
Proximate  Elements  of  organized  bodies.  Of  these  proximate 
elements.  Sugar,  Oil,  Albumen,  &lq,.  are  familiar  examples. 

Perhaps  it  may  be  stated  as  a  general  law,  that  no  substance, 
entering  into  the  composition  of  a  living  plant  or  animal,  is  so 
pure  as  to  be  capable  of  assuming  a  reguhirly  crystallized  form. 
Instead,  therefore,  of  being  defined  by  straight  lines  and  angles, 
almost  all  solid  organized  substances  are  more  or  less  rounded, 
and  their  intimate  structure  is  anything  but  crystallized.  The 
composition  of  organized  fluids  is  equally  heterogeneous  ;  and 
though  the  basis  of  nearly  every  one  of  such  fluids  be  water, 
many  of  them  contain  a  variety  of  other  matters. 

Organized  bodies  may  be  ranged  under  two  general  classes  ; 
those  which  though  they  do  not  crystallize,  while  in  the  living 
plant  or  animal,  can  yet,  by  various  processes,  be  so  far  separated 
from  extraneous  matters,  as  to  be  obtained  in  a  state  of  purity, 
and  thus  be  made  to  assume  the  crystallized  form  ;  and  those 
which  cannot  under  any  circumstances  be  made  to  crystallize. 
The  first  substance  of  the  crystallizable  class  which  we  shall 
notice,  is  Sugar. 

Sugar  has  been  ascertained,  and  is  now  generally  admitted,  to 
consist  of  three  essential  elementary  principles — hydrogen,  oxy- 
gen, and  carbon  ;  it  is  besides  remarkable,  that  the  hydrogen  and 
the  oxygen  in  sugar  are  exactly  in  the  proportion  to  each  other, 
in  which  they  form  water.     It  has  been,  therefore,  with  great 
probability  inferred,  that  these  two  elements  are  really  so  asso- 
ciated in  sugar;  consequently,  that  sugar  is  a  compound  of  water 
and  carbon  ;  or,  in  the  language  of  Chemists,  is  a  Hydrate  of 
Carbon.      We  cannot,  however,  produce  artificially  either  sugar, 
or  any  other  organic  compound,  by  directly  combining  their  ele- 
ments ;  because  we  cannot  bring  the  elements  together,  precisely 
in  the  requisite  stales  and  proportions.     Still,  there  is  no  doubt, 
that  if  the  elements  could  be  so  brought  together,  the  compound 
thence  resulting,  would  be  the  same  as  the  natural  compound. 
For,  as  hereafter  we  shall  endeavour  to  show,  the  organic  agent 
does  not  change  the  properties  of  the  elements  ;  but  simply  com- 
bines them  in  modes  which  we  cannot  imitate. 

Vinegar  is  another  well  known  proximate  principle,  which 
not  only  forms  crystallized  compounds  readily  with  many  other 
bodies  ;  but  in  its  most  concentrated  state,  is  itself  also  crystal- 
lized. Now,  it  is  not  less  worthy  of  note  than  in  the  case  of 
sugar,  that  vinegar,  altogether  so  diflerent  from  sugar  in  its  pro- 
pcrlies,  is  generally  considered  to  be  precisely  analogous  in  its 
composition  ;  that  is  to  say,  vinegar  is  a  binary  compound  of 
water  and  carbon  ;  but  the  proportions  of  water  and  carbon  are 
diflerent  from  those  that  form  sugar.     There  is  however,  a  cha- 


1 


COMPOSITION  OF  ORGANIZED  BODIES.  231 

racleristic  distinction  between  these  two  substances,  inasmuch  as 
vinegar  can  be  formed  artificially  ;  not  indeed,  any  more  than 
sugar,  by  directly  associating  its  elements  :  but,  by  the  process 
of  fermentation,  and  by  other  means,  this  acid  may  be  formed 
from  sugar  and  from  the  allied  substances  to  be  presently  men- 
tioned. Yet  we  cannot  work  backwards,  and  by  any  artificial 
process  again  form  sugar  from  vinegar  ;  though  the  organic  agent 
seems  to  possess  this  power,  as  we  shall  have  occasion  to  notice 
more  particularly  hereafter. 

We  now  proceed  to  consider  the  composition  of  a  totally  dif- 
ferent class  of  substances,  which  under  no  circumstances,  natural 
or  artificial,  ever  assume  the  crystallized  form  ;  and  the  struc- 
ture  of  which,  in  the  common  and  strict  snnse  of  the  term,  may 
be  said  to  be  organized.  Starch  is  a  well  knov/n  instance  of 
these  uncrystallizable  or  organized  substances. 

Tiie  amylaceous  or  starchy  principle  is  obtained  in  slightly 
modified  states,  from  a  great  variety  of  vegetables,  but  princi- 
pally from  the  seeds  of  the  Cerealia.  Even  by  the  unassisted 
eye,  starch  is  seen  to  be  composed  of  minute  particles ;  and 
when  these  particles  are  examined  with  a  microscope,  they 
are  found  to  be  granules  more  or  less  rounded,  and  without  the 
least  trace  of  crystallization.  These  granules  are  conceived  to  be 
moulded  in  the  cellules  of  the  texture  by  which  they  are  formed  ; 
for  it  would  appear  that  their  state  when  first  secreted  and  de- 
posited in  the  cpUnles  is  semifluid  ;  and  that  the  excess  of  wat?y 
is  subsequently  removed.  Raspaii  and  Dumas  have  shown  that 
each  of  these  little  grains  is  covered  with  a  smooth  integument,  not 
afiected  by  water  at  the  common  temperatures  ;  within  which  in- 
tegument is  enclosed  a  substance  rather  more  soluble.     According 

1        •  •  • 

to   some  chemists,  this  interior  substance  has  an  analogy  with 

gum;  but  probably  it  is  only  a  variety  of  amylaceous  matter. 
Berzelius  affirms  that  starch  when  burnt,  leaves  about  .23  per 
cent  of  residuum,  consisting  entirely  of  the  phosphates.  But 
when  this  residuum  is  abstracted  and  allowed  for,  the  essential 
composition  of  starch  is  found  to  coincide  very  nearly  with  that 
of  sugar;  that  is  to  say,  starch  is  composed  of  water  and  carbon, 
and  the  proportions  of  their  combination  are  very  nearly  the  same 
as  in  sugar.  Here  a  question  arises  :  How  does  it  happen  that 
substances  which  appear  to  resemble  each  other  so  closely  in 
their  composition,  should  yet  difier  so  widely  in  their  sensible 
properties  ?  This  question  we  shall  soon  consider.  But  in  the 
mean  time,  we  shall  make  a  few  remarks  on  another  principle  of 
organized  bodies,  still  very  different,  in  its  sensible  properties, 
from  the  three  of  which  we  have  spoken,  but  apparently  of  a 
similar  constitution.  This  fourth  principle  is  the  ivoody  fibre,  or 
Lignin,  as  it  is  termed  by  chemists. 


232 


CHEMISTRY  OF  ORGANIZATION. 


The  woody  fibre,  though  assuming  a  great  variety  of  appear- 
ances in  different  plants,  and  including  very  different  incidental 
matters  ;  has  nevertheless,  in  all  those  plants  in  which  it  has  yet 
been  examined,  been  found  to  possess  very  nearly  the  same  es- 
sential composition  ;  or  to  consist  of  equal  weights  of  water  and 
of  carbon.  Such,  at  least,  is  the  composition  of  woods,  so  very 
different  as  the  Box  and  the  Willow,  the  Oak  and  the  Beech  ; 
and  these  are  the  chief,  if  not  the  whole,  of  the  woods  which,  we 
believe,  have  yet  been  analyzed.  Hence,  it  is  perhaps  not  un- 
reasonable to  suppose  that  every  variety  of  Lignin  has  a  similar 
composition.  All  woods,  when  burnt,  leave  a  greater  or  less 
quantity  of  incidental  mineral  residuum,  in  the  shape  of  ashes  ; 
the  nature  of  which,  as  above  observed,  differs  exceedingly  in 
different  sorts  of  wood. 

The  following  Table  presents  a  summary  view  of  the  compo- 
sition of  tlie  four  organic  principles  which  we  have  considered  in 
the  preceding  paragraphs.  It  is  offered,  not  only  as  an  example 
of  the  boundless  subject  of  the  Chemistry  of  Organization,  but 
as  an  instance  of  the  mode  by  which  we  conceive,  that  depart- 
ment of  Chemistry  may  be  best  elucidated. 


Substances  Crystallizable. 

Substances  not  Crystallizable. 

Sugar,  from 

Carbon. 

Water. 

t 
Starch,  Arrow- 

Carbon. 

Water. 

Starch  -   - 

36.20 

63.80 

root  in    its 

from  Honey 

3G.36 

63.63 

ordinary 

East  India 

state      -   - 

36.4 

63.6 

Moist    -   . 

40.88 

59.12 

from     Wheat, 

Beet  root  and 

in  its  ordi- 

IMaplc  -    - 

42.10 

57.90 

nary  state 

37.5 

62.5 

Enjrlisli  Re- 

ditto, ditto, 

fined  -   -   - 

41.5  to  42.5 

58.5  to  57.5 

dried  at 

Pure  Suj^ar 

212°      -   - 

42.8 

57.2 

Candy  -    - 

42.85 

57.15 

Acetic  Acid  - 

47.05 

52.95 

Lignin,  in  its  or- 
dinary stale 

of  dryness 

42.7 

57.3 

from  Willow, 

dried  at 

212°. 

49.8 

50.2 

from  Box,  do 

50 

50 

A  cursory  inspection  of  the  foregoing  Table  will  evince  to  the 


C0I»1P0SITI0N  OF  ORGANIZED  BODIES.  233 

reader,  how  nearly  the  general  composition  of  sugar  and  of  starch 
agree  together ;  and  that  the  agreement  extends  even  to  their 
several  varieties.  Vinegar,  or  acetic  acid,  has  not,  at  present, 
any  known  representative,  among  other  organic  principles  ; 
though  it  is  not  improbable  that  several  substances  exist  of  con- 
formable proportions.  The  composition  of  vinegar,  or  acetic 
acid,  is  intermediate  to  that  of  sugar  and  of  Lignin  ;  while  among 
crystallizable  organic  substances,  there  is  no  known  compound 
analogous  to  Lignin.  It  may,  at  the  same  time,  be  remarked, 
that  both  starch  and  wood  can,  by  difi'erent  artificial  processes, 
be  converted  either  into  sugar  or  into  vinegar.  We  can  also  con- 
vert wood  into  a  sort  of  starch,  as  we  may  convert  sugar  into 
vinegar ;  but  we  are  unable  to  reverse  the  process,  and  convert 
vinegar  into  sugar,  or  starch  into  wood  ;  though  these  and  innu- 
merable changes  of  a  similar  kind  are  easily  affected  by  organic 
agency. 

We  proceed  now  to  consider  briefly  the  question  we  have 
already  stated, 

2.  How  does  it  happen  that  substances,  so  nearly  allied  in 
their  composition,  exhibit  sensible  properties  so  entirely  differ- 
ent?— This  question,  in  all  its  bearings,  is  probably  beyond  our 
powers  of  investigation  :  at  least  the  extent  of  the  requisite  know-- 
ledge  we  have  yet  attained,  must  be  allowed  to  be  exceedingly 
inadequate.  The  few  observations  which  we  have  to  offer  re- 
garding this  question  may  be  comprised  under  the  two  following 
heads : — The  peculiarity  of  the  composition  of  organic  sub- 
stances ;  and  the  nature  of  the  agents  by  which  these  substances 
are  produced. 

The  composition  of  organized  bodies  may  be  viewed  as  of  two 
general  kinds,  viz.  their  composition,  as  depending  simply  upon 
differences  among  the  proportions  of  their  essential  elements  ; 
and  their  composition  as  depending  upon  differences  among  their 
incidental  elements,  the  proportions  of  the  essential  elements  being 
the  same.*  As  instances  of  the  first  kind  of  composition,  we 
may  mention  sugar  and  vinegar.  Thus,  sugar  is  composed  of 
42.85  per  cent  of  carbon,  and  the  rest  water ;  while  the  same  in- 
gredient, carbon,  in  the  larger  proportion  of  47.05  per  cent,  with 
the  residue  water,  constitutes  vinegar,  a  powerful  acid.  Why, 
with  such  similarity  of  composition,  the  sensible  properties  of 
these  two  substances   should  be   so  unlike,  we  know  not ;  any 

*  Of  course  there  is  a  third,  and  perhaps  the  most  extensive  class  of 
bodies,  hi  which  both  the  essential  and  the  incidental  elements  may  be 
supposed  to  vary  ;  but  partly  from  want  of  data,  and  partly  to  avoid  too 
much  complication,  we  shall  not  enter  upon  the  consideration  of  this  class 
at  present. 

30* 


234  CHEMISTRY  OF  ORGANIZATION. 

more  than  we  know  why  oxygen  and  hydrogen,  when  combined, 
form  water,  or  than  we  know  any  ultimate  chemical  fact.  How- 
ever wonderful,  therefore  the  results  of  these  slight  differences  of 
composition  may,  at  the  first  view,  appear  ;  a  little  reflection 
will  convince  us,  that  in  reality,  they  are  not  more  wonderful 
than  any  other  chemical  phenomenon;  and  that  they  only  form 
a  particular  variety  of  such  phenomena.  The  same  remarks  are 
applicable,  in  part  at  least,  to  the  striking  dilTerences  exhibited 
by  Sugar  and  Starch  ;  the  essential  composition  of  which  two 
substances,  as  we  have  before  observed,  is  nearly  the  same  ;  but 
the  starch  contains  incidental  bodies,  from  which  the  sugar  is 
free.  On  the  operation  of  these  incidental  bodies  we  shall  ofl'er 
a  few  conjectural  remarks. 

At  the  commencement  of  this  chapter,  we  stated  that  the  inci- 
dental substances  existing  in  organized  bodies  have  hitherto  been 
considered  as  foreign  ;  but  that  we  could  not  subscribe  to  that 
notion.  We  may  now  observe,  that  they  seem  to  us,  to  contri- 
bute chiefly  towards  the  production  of  those  striking  differences, 
observed  among  bodies  having  the  same  essential  composition  ; 
and  which  diversity,  at  first  sight,  appears  so  mysterious.  How 
these  minute  quantities  operate  we  do  not  precisely  understand  ; 
but  we  can  imagine  them  to  be  interposed  among  the  constituent 
molecules  :  further,  that  the  molecules  of  these  incidental  matters 
are  in  a  state  of  strong  self-repulsion.  Such  being  the  case,  it  is 
not  unreasonable  to  expect  that  they  may  have  the  power  of 
modifying  the  arrangement  of  the  constituent  molecules  ;  and  thus 
of  altering  the  sensible  properties  of  the  substance  produced  by 
their  combination. 

We  have  stated  our  opinion  that  the  molecules  of  incidental 
matters  in  organic  substances  are  in  a  state  of  self-repulsion. 
This  opinion  is  founded  principally,  on  the  equal  diffusion  of 
these  im'idenlal  molecules  throughout  the  organic  substances  in 
which  they  exist ;  and  on  their  consequent  great  distance  from 
eacli  other,  which,  perhaps,  can  hardly  be  otherwise  explained. 
If  these  incidental  matters  were  detached,  or  merely  in  a  state  of 
mixture  with  the  constituent  elements,  as  is  implied  in  the  notion 
of  their  being  foreign,  they  would  probably  retain  tlieir  self-at- 
tractive powers  ;  and  instead  of  being  equally  diffused  among 
the  constituent  elements,  they  would  be  collected  together  into  a 
mass  or  crystal ;  an  arrangement  never  observed.  For,  though 
crystallized  bodies  are  found,  not  unfrequently,  within  organized 
substances;  yet  these  bodies  are  always  extraneous,  and  do  not 
form  any  part  of  llic  living  structure ;  of  which,  the  molecules  un- 
der our  consideration  do  actually  appear  to  be  integrants.  In  further 
corroboration  of  this  opinion,  may  be  adduced  the  beautiful  ex- 
periments of  Sir  John   llerschel,  who  has  shown,  that  an  enor- 


COMPOSITION  OF  ORGANIZED  BODIES.  235 

mous  power,  not  less  than  50,000  times  the  power  of  gravity,  is 
instantaneously  generated  by  the  simple  agency  of  common  mat- 
ters submitted  to  galvanic  influence  ;  as,  for  example,  by  the 
agency  of  mercury  alloyed  with  a  millionth  part  of  its  weight  of 
sodium.  These  facts,  while  they  place  beyond  all  doubt,  the 
efficacy  of  minute  quantities  of  matter,  in  producing  the  most 
extraordinary  change  of  the  polarities  of  larger  quantities  ;  at  the 
same  time  appear  to  throw  great  light  on  many  natural  opera- 
tions. Tims  the  subtle  matters  of  contagion  and  miasmata ;  va- 
rious medicinal  substances,  whose  effects  are  most  astonishing 
even  in  the  smallest  doses  ;  the  still  more  refined  and  recondite 
mr*»ers  of  heat  and  of  light,  with  many  others,  all  probably  act 
on  .'imilar  principles.  At  least,  the  results  of  the  operation  of 
th^  fie  matters  cannot  be  explained  by  iheir  mere  quantity  ;  which 
ir'^the  ordinary  chemical  acceptation  of  the  term,  is  altogether  in- 
commensurate with  the  evident  and  striking  changes,  constantly 
arising  in  the  processes  of  nature,  from  such  agency. 

The  observations  that  have  now  been  offered,  are  intended  to 
apply  to  all  those  elementary  substances,  entering  into  the  com- 
position of  a  living  organized  being.  For,  no  one  element,  when 
thus  assimilated,  appears  to  be  in  its  natural  state ;  or  to  be  ca- 
pable of  exerting  precisely  those  powers  which  it  is  known  to 
exert,  when  acting  in  virtue  of  its  original  inorganic  properties. 
In  sbort,  we  may  thus  recapitulate  what  has  been  said  :  besides 
the  essential  molecules  constituting  the  ground-work  of  a  living 
organized  being,  and  which  probably  exert  on  each  other,  to  a 
certain  extent,  the  ordinary  chemical  influences  of  matter ;  it 
-would  seem  that  there  are,  at  the  same  time,  diffused  throughout 
the  whole  living  mass,  in  exceedingly  minute  proportion,  va- 
rious other  matters,  the  molecules  of  which  appear  to  be  in  a 
high  state  of  self-repulsion.  By  these  incidental  matters,  it 
would  further  seem,  that  the  ordinary  chemical  properties  of  the 
essential  elements  of  the  organized  living  structure  are  variously 
modified  ;  in  particular,  that,  the  essential  elements  are  hindered 
from  assuming  a  regularly  crystallized  form.  Moreover,  these 
incidental  matters  entering  into  the  composition  of  a  living  body, 
apparently  furnish  to  the  organic  agent  new  powers  utterly  beyond 
our  comprehension  ;  which  powers  the  organic  agent  has  been 
endowed  with  the  ability  to  control,  and  direct,  in  any  manner 
that,  from  the  exigencies  of  the  living  organized  being,  may  be- 
come requisite.* 

The  intimate  nature  of  the   organic  agent  or  agents^  or  by 

*  In  addition  to  what  is  stated  in  the  text,  we  may  remind  the  reader 
of  what  we  have  elsewhere  alluded  to,  viz . :  that  the  organic  agents  have 


236  CHEMISTRY  OF  ORGANIZATION. 

whatever  other  name  we  may  choose  to  designate  the  peculiar 
enero^ies  which  exist  in  plants  and  in  animals,  and  by  which  they 
are  distinguished  from  inanimate  matter,  is  now,  and  probably 
will  ever  remain,  altogether  unknown  to  us.  But  though  we  be 
thus  ignorant  of  what  these  agents  are  i  we  can  not  only  com- 
prehend with  tolerable  certainty,  what  they  are  not ;  but  we  can 
also  in  some  degree  ascertain,  what  they  are  capable  or  incapa- 
ble of  eflecling.  As  it  is  of  the  utmost  consequence  to  obtain 
just  views  on  these  points,  we  shall  consider  them  somewhat  in 
detail. 

When  we  were  treating  of  inorganic  elements  and  agencies,  and 
of  the  laws  which  they  appear  mutually  to  obey,  we  found,  that 
though  their  nature  be  obscure,  and  the  investigation  of  them  very 
difficult ;  we  were  nevertheless  enabled  to  adduce  some,  not  al- 
together unplausible,  conjectures  on  the  modes,  in  which  the  ele- 
ments combine,  to  form  regular  crystals  and  the  other  conditions 
of  inanimate  matter.  Now  with  this  insight  into  the  nature  of 
inorganic  operations,  and  with  all  the  additional  knowledge  of 
every  kind  that  we  can  command,  let  us  attentively  survey  the 
most  simple  plant  or  animal ;  let  us  observe  the  actions,  the 
changes,  the  modifications  of  form  and  properties  it  continually 
exhibits  ;  and  then  let  us  seriously  ask  ourselves,  whether  every- 
thing that  we  know,  will  enable  us  to  make,  even  an  approach, 
toward  an  explanation  of  what  we  see.  It  is  indeed  true,  that 
the  plant  or  animal  we  examine  is  composed  of  charcoal  and 
water,  and  of  other  ingredients  with  which  we  are  equally  fami- 
liar ;  that  it  is  liable  to  be  afiected  by  Heat,  Light,  Electricity, 
and  by  other  inorganic  agents.  But  it  is  perfectly  ascertained 
that  these  elements  and  agents,  out  of  an  organized  body,  and 
left  enlirelij  to  themselves^  never  would  or  could  unite,  either  in 
virtue  of  their  own  properties,  or  from  accident,  so  as  to  form  any 
j)lant  or  ajiimal  however  insignificant.  Are  we  not  then  compell- 
ed to  infer,  that  within  a  plant  or  animal,  there  exists  a  principle 
or  agent  superior  to  those  whose  operations  we  witness  in  the 
inorganic  world;  and  which  agent  moreover  possesses,  under  cer- 
tain restraints,  the  power  of  controlling  and  directing  the  opera- 
tions of  these  inferior  agents?  That  this  is  a  natural  and  a  just 
inference,  no  one  who  calmly  views  all  the  circumstances  will 
ever  deny  ;  and  if  the  existence  of  one  such  agent  be  admitted, 
the  admission  of  the  existence  of  others  can  scarcely  be  withheld  ; 
for  the  existence  of  one  only,  is  quite  inadequate  to  explain  the 

probably  tlie  power,  within  certain  limits,  of  separating  the  molecules  of 
bodies,  considered  at  present  as  elementary,  into  more  refined  forms  of 
matter  (submolcculcs  •'). 


COMPOSITION  OF   ORGAMZED  BODIES.  237 

infinite  diversity  among  plants  and  animals.  Thus,  in  the  words 
of  tlie  excellent  Paley,  "  there  may  be  many  such  agents',  and 
many  ranks  of  them:"  in  other  words,  there  may  be  an  ascend- 
ing gradation  of  these  agents,  from  that  of  the  comparatively 
simple  plant,  onward  to  that  of  the  most  complicated  animal. 

Such  being  the  suggestions  concerning  organic  agency  that 
arise  from  a  general  survey  of  organic  operations  ;  let  us,  with 
reference  to  the  further  bearing  and  tendency  of  these  sugges- 
tions, inquire  a  little  more  minutely  into  the  powers  and  modes 
of  operation  of  organic  agents. 

3.  Of  the  modes  of  Operation  of  Organic  Agents. — In  the 
first  place,  with  regard  to  what  cannot  be  effected  by  organic 
agency,  we  may  observe,  that  no  organic  agent  has  the  power 
either  of  creating  material  elements,  or  of  cJianging  one  such 
element  into  anotiier.  By  element,  it  maybe  right  to  premise,  is 
here  meant,  a  principle  that  is  not  made  up  of  others  ;  and  which, 
consequently,  possesses  an  absolute  and  independent  existence. 
Whether  one,  or  more,  such  elements  exist,  it  is  not  now  our  ob- 
ject to  inquire.  The  astonishing  discoveries  of  modern  chemis- 
try have  shown,  that  many  of  those  substances,  formerly  consi- 
dered as  elements,  are,  in  fact,  compounds  ;  and  as  the  science 
of  chemistry  is  still  progressive,  it  is  probable  that,  with  the 
enlargement  of  its  boundaries,  there  will  be  a  still  further  di- 
minution of  the  number  of  those  substances  which  are,  as  yet, 
held  to  be  simple.  Admitting,  however,  for  the  sake  of  argu- 
ment, that  elementary  principles  do  exist,  of  such  immutable 
character  as  has  been  supposed  ;  from  the  nature  of  organic 
beings,  at  least  of  all  animals,  it  is  impossible  to  conceive  that 
they  possess  the  power  either  of  creating  or  of  altering  these  ele- 
mentary principles.  For  no  organized  being  has  an  independent 
existence,  but  all  animals  derive  their  support  from  previous  or- 
ganization, which  might  be  otherwise,  did  they  possess  a  creating 
power  ;  nor  can  they  be  nourished  by  ail  substances  indiscrimi- 
nately, as  they  ought  to  be,  were  they  possessed  of  a  transmuting 
power.  Yet,  while  it  is  thus  denied  that  organized  beings 
possess  the  power,  either,  to  create  or  to  change,  in  the  strict  ac- 
ceptation of  these  terms  ;  it  has  been  admitted  to  be  exceedingly 
probable,  that  the  organic  agent  is,  within  certain  limits,  qualified 
to  compose  and  decompose  many  substances  which  are  now 
viewed  as  elements  ;  and  that  the  organic  agent  does  thus  ap- 
parently form  and  transmute  these  imagined  elements.  But  to 
enter  further,  in  this  place,  on  the  elucidation  of  these  obscurities 
would  be  foreign  to  our  present  purpose. 

The  organic  agent  has  not  the  power  of  combining  elements 
in  such  a  manner,  that  the  properties  of  the  resulting  compound 
shall  differ  from  those  of  a  compound,  formed  from  the  same 


238  CHEMISTRY  OF  ORGAMZATION. 

elemeiiis  similarly  combined  by  any  other  agent.  The  Deity  has 
cliosen  to  prescribe  limits  to  his  power,  and  to  establish  certain 
laws,  to  which  He  at  all  times  rigidly  adheres  ;  and,  again  adopt- 
ing the  language  of  Paley,  "  when  a  particular  purpose  is  to  be 
effected,  it  is  not  by  making  a  new  law,  nor  by  the  suspension 
of  the  old  ones,  nor  by  making  them  wind,  and  bend,  and  yield 
to  the  occasion  ;  but  it  is  by  the  interposition  of  an  apparatus 
corresponding  with  those  laws,  and  suited  to  the  exigency  which 
results  from  them,  that  the  purpose  is  at  length  attained."  In  the 
instance  before  us,  the  attainment  of  the  particular  purpose  of 
organic  life  is  effected,  not  by  any  departure  from  the  great 
scheme,  but  by  new  and  different  combinations.  To  suppose, 
therefore,  that  the  organic  agent  can,  for  example,  combine  oxy- 
gen and  hydrogen,  in  exactly  tlie  same  proportion,  and  in  the 
same  manner,  in  which  they  are  combined,  when  they  exist  as 
Avater ;  and,  from  these  elements  so  combined,  can  yet  produce 
something  different  from  water,  is  contrary  to  all  reason,  and 
wo  jld  be,  in  truth,  to  accuse  the  Deity  of  subverting,  and  of  act- 
ing in  opposition  to,  his  own  laws.  We  have  dwelt  the  more 
strongly  on  these  points,  because  among  physiologists  a  vague 
notion  seems  to  have  prevailed,  that  organic  agents  have  the 
power,  not  only  of  changing  the  inherent  and  peculiar  properties 
of  bodies  ;  but  likewise,  of  causing  the  results  of  their  combina- 
tion to  be  altogether  different  from  those  that  are  produced,  under 
exactly  similar  circumstances,  by  inorganic  agency.  If  however 
the  arguments  we  have  advanced  be  well  founded,  this  notion 
must  be  erroneous  ;  and  its  erroneous  character  will  be  rendered 
still  more  evident,  by  the  observations,  we  shall,  in  the  second 
place,  offer,  regarding  the  principles  on  which  the  operations 
within  living  organized  bodies  are  really  conducted. 

Tiie  means  by  which  organic  agents  accomplish  the  purpose 
for  which  they  are  designed,  may  be  naturally  divided  into  two 
kinds  ;  those  which  are  dependent  on  peculiarity  of  composition 
and  of  structure  ;  and  those  by  which  tJiis  peculiarity  of  com- 
position and  of  structure  is  produced. 

hupiiry  into  the  first  of  these  means  of  action  has  already 
been  in  great  degree  anticipated.  A  brief  recital,  therefore,  is  all 
that  is  here  necessar3^  We  have  seen  that  organized  substances 
are  composed  of  the  same  elements,  which  exist  abundantly 
throughout  the  world  in  the  inorganized  state  ;  moreover  that 
these  elements  are  subject  to  all  the  influences  and  agencies  of 
inorganic  nature.  We  have  seen  that  organic  agents  are  enabled 
to  form  certain  proximate  principles,  by  variously  combining  their 
elements  ;  whicii  proximate  principles,  even  when  in  the  con- 
dition of  crystals,  it  is  not  possible  to  imitate  artificially.  We 
have,  at  the  same  time,  seen  that  these  proximate  principles, 


COMPOSITION  or  ORGANIZED  BODIES.  239 

though  they  may  have  a  riatural  tendency  to  crystallize,  are,  as 
they  usually  exist  in  living  bodies,  prevented  from  undergoing 
that  process,  by  the  diffusion  of  minute  quantities  of  other  ele- 
ments throughout  their  mass  :  the  molecules  of  which  are  in  some 
unknown  state  of  activity  ;    such   perhaps   as  cannot  naturally 
exist  in  the  universe,  except  when   conjoined  with  organization. 
Finally,  we  have  inferred,  that  the  differences  and  peculiarities 
of  these  minute   additional    matters,  are  probably  adequate    for 
explaining  the  differences  and  peculiarities,  of  the  sensible  and 
chemical  properties  of  the  substances  that  are  formed  by  organi- 
zation.    Having  thus  pointed  out  the  general  differences  of  com- 
position existing  among  organized  bodies;  it  remains  to  state,  that 
such  differences  of  composition  almost  invariably  indicate    dif- 
ferences of  structure.     For  though  similarity  of  composition  does 
not  necessarily  imply  similarity  of  structure  ;   yet  similarity  of 
structure    perhaps,  without   exception,  indicates    similarity,    or, 
at  least,  analoi^y  of  com.position  ;    and,  consequently,  similarity 
of  action.     Thus  the  woody  fibre  of  plants  is  always  formed  of 
the  principle  termed  Lignin,  and  never  of  resin,  or  of  albumen. 
The   relation   of  structure  to  chemical  composition  is   not  less 
striking  in  tb.e  muscular  fibres  of  animals,  and  indeed  in  all  or- 
ganic compounds  of  a  definite  character  ;    the  essential  composi- 
tion* of  such  substances,  though  exhibiting  endless  minor  diver- 
sities, being  nevertheless,  in  all  instances,  precisely  the  same. 

The  means  by  which  that  peculiarity  of  cotnposition  and  of 
structure  is  produced,  which  is  so  remarkable  in  all  organic  sub- 
stances, like  the  results  themselves,  are  quite  peculiar  ;  and  bear 
little  or  no  resemblance   to  any  artificial  process  of  chemistry. 
For  example,  we  have  not,  in  artificial  chemistry,  any   control 
over  individual  molecules  ;  but  are  obliged  to  direct  our  opera- 
tions   on   a  mass,    formed    of  a    large   collection    of  molecules. 
The  organic  agent,  on  the  contrary,  having  an  apparatus  of  ex- 
treme minuteness,  is  enabled  to  operate  on  each  individual  mole- 
cule separately  ;   and  thus,  according   to    the   object  designed,  to 
exclude  some  molecules,  and  to  bring  others  into  contact.     In 
these  processes,  it  may  be  conceived,  that  the  molecules  thus 
•appropriately  brought  together,   and,  at  the  same  time,  guarded 
from   extraneous  influence,  by  the  organic  agent,  are  in  virtue  of 
their  own  proper  aihnities,  sufficiently  disposed  to  unite,  without 
requiring  that  any  new  properties  should  be  communicated  to 
them.     Hence   the   organic   agent,  in  its   simplest  state,  may  be 
viewed  as  a  power  which  so  controls  certain  inorganic  matters, 
as  to  form   them  into  an  apparatus,  by  which  it  arranges  and  or- 
ganizes other  matters,  and  thus  effects  its  ulterior  purposes.  Where 
the  operations  of  this  simple  organic  agent  terminate,  those  of 
another  and  more  effective  organic  agent  may  be  supposed  to 


240  CHEMISTRY  OF  ORGANIZATION. 

beo-in  ;  which,  by  carrying  the  general  process  of  organization  a 
step  further,  adapts  the  organized  material  for  the  operations  of  a 
third  and  yet  higher  agent.  Thus,  each  new  agent  may  be  sup- 
posed to  possess  more  or  less  control  over  all  those  below  itself, 
and  to  have  the  power  of  appropriating  their  services  ;  till  at 
length,  at  the  top  of  the  scale,  we  reach  the  perfection  of  organized 
existence.  The  excellent  Paley  sanctions  this  view  of  organic 
operations,  and  continues  in  the  following  words  :  "  We  do  not 
advance  this  as  a  doctrine  either  of  philosophy  or  of  religion  ;  but 
we  say  that  the  subject  may  safely  be  represented  under  this 
view  ;  because  the  Deity,  acting  himself  by  general  laws,  will 
have  the  same  consequences  upon  our  reasoning,  as  if  he  had 
prescribed  these  laws  to  another."  . 

This  view  of  the  successive  creation  of  organic  agents,  which 
harmonizes  not  only  with  the  phenomena  of  Geology,  but  with 
the  differences  which  are  observable  among  plants  and  animals, 
and  with  the  developement  of  the  more  perfect  species  ;  is  directly 
opposed  to  the  notion  of  spontaneous  developement  maintained 
by  some  distinguished  French  philosophers  ;  as  well  as  to  the 
opinion  that  life  is  the  result  of  organization.  Thus  we  consider 
it  impossible  that  by  any  accidental  concurrence  of  circumstances, 
a  dog  can,  in  the  progress  of  time,  be  gradually  converted  into  an 
ape,  or  an  ape  into  a  man ;  and  moreover,  we  not  only  think  such 
an  hypothesis  directly  at  variance  with  the  whole  tenor  of  the  laws 
of  nature,  but  quite  absurd.  The  laws  of  nature,  as  we  have  shown, 
are  in  all  cases  most  rigidly  adhered  to  by  the  Deity.  These 
laws,  therefore,  are  unalterably  stable,  within  the  limits  that  have 
been  assigned  to  them.  Now,  from  what  we  know  of  the  laws 
of  nature,  or  of  the  properties  of  the  elements  of  matter,  or  of  the 
agents  by  which  they  are  moved,  it  is,  as  we  have  already  stated, 
impossible  to  conceive  that  carbon,  water,  and  electricity,  of  their 
own  accord,  and  from  any  inherent  influence,  can  so  unite  as  to 
form  the  humblest  plant  or  animal;  much  less,  so  as  to  secure  its 
perpetual  existence  by  reproduction.  For  similar  reasons  it  is 
equally  impossible  to  conceive,  that  there  can  ever  be  such  a  spon- 
taneous arrangement  or  combination  of  inferior  organic  agents, 
as  to  foim  a  superior  agent.  Whenever,  therefore,  a  new  and 
specific  agent  is  required,  a  new  and  specific  act  of  creation  must 
be  performed  by  the  Great  Architect  of  the  universe.  Nearly  si- 
milar remarks  apply  to  the  opinion  that  the  living  principle  is  the 
result  of  organization.  The  living  principle  is  not  the  result  of 
organization,  but  the  cause  of  organization.  In  accounting  for  the 
phenomena  of  life,  it  is  absolutely  necessary  to  assume  the  exist- 
ence of  some  agency  different  from,  and  superior  to,  that  which 
operates  among  inorganic  matters.  Now  since,  as  we  have  seen, 
no  inferior  agencies  can  be  supposed  so  to  combine  as  to  form  a 


COMPOSITION  OF  ORGANIZED  BODIES.  241 

superior  agency;  does  it  not  accord  better  with  our  reason,  as  well 
as  with  our  experience,  to  assume  at  once  a  new  creation  of  the 
higlier  principle  ? 

The  first  circumstance  that  arrests  our  attention,  with  reference 
to  the  preceding  remarks,  is  the  wonderful  adaptation  of  the  ele- 
ments and  the  agents  of  organic  nature  to  each  other.     For  exam- 
ple, had  not  carbon,  and  azote,  and  water,  been  formed  with  the 
properties  which  they  now  possess,  organic  agents,  as  we  know 
them,  would  have  existed  in  vain  ;  and  without  organic  agents, 
the  properties  of  these  elements  would  equally  have  been  useless. 
And  how  truly  wonderful,  and  utterly  beyond  our  comprehension, 
are  the  properties  and  adaptations  displayed  in  the  processes  of 
organization  !     To  enable  ourselves  to  form  some  conception  of 
these  processes,  by  bringing   to  a  level  with  our  understanding, 
those  things  which  they  accomplish  ;  let  us  propose  to  ourselves 
the  question, — What  ought  to  be  the  inherent  properties  and  the 
constitution  of  an  elementary  principle,  which  should  not  only  be 
capable  of  being  formed  into  the  hardest  and  the  softest  bodies  in 
nature;  but  which  should  also  be  capable  of  entering  as  an  essen- 
tial ingredient  into  substances  so  very  unlike,  as  sugar,  vinegar, 
wood,  oil,  albumen,  and  many  others,  in  all  their  countless  forms 
and  varieties?     Do  we  not  feel  all  our  fancied  knowledge  annihi- 
lated by  such  a  question  ?     Nay  what  is   more,  even   when  the 
question  is  answered  fur  us  ;  and  when,  with  the  utmost  care,  and 
to  the  furthest  extent  of  our  ability,  we  have  studied   all  the  che- 
mical properties  of  Carbon — the  substance  by  which  the  condi- 
tions of  the  question  are  fulfilled ;  how  totally  unable  are  we  to  ex- 
plain these  properties,  or  even  to  trace  them  through  their  simplest 
modifications  ?    Why,  for  instance,  is  the  diamond  capable  of  as- 
suming the  form  of  charcoal ;  or  why  is  charcoal  capable  of  as- 
suming the  form  of  the  diamond?     And  how  are  these  properties 
modified,  and  altered,  in  all  the  numerous  states  of  combination 
into  which  we  know  carbon  enters  ?  On  what  property  or  quality, 
not  possessed  by  other  elements,  do  all  those  astonishing  capabi- 
lities of  change  depend,  which  are  inherent  in  this  element  carbon? 
And  why  has  carbon  been  chosen  for  forming  organized  beings, 
in  preference  to  silex,  or  iron,  or  any  other  element?*    To  us  all 

*  Since-  there  is  nothing  peculiar  in  the  elements  of  which  organized 
beings  are  composed,  and  no  reason  can  be  assigned  why  carbon  and  other 
elements  have  been  cliosen  for  their  formation,  we  are  compelled  to  as- 
cribe the  choice  of  these  materials  to  the  will  of  the  Great  Creator.  But 
as  He  never  acts  without  a  purpose,  we  cannot  doubt  that  these  elements 
have  been  selected  for  some  specific  design  ;  which  design  has  probably 
been,  that  the  fabric  of  the  beings  dwelling  on  this  earth,  might  be  adapt- 
ed to  its  general  position  in  the  Solar  system.  When  we  consider  that 
the  same  heat,  and  the  same  light  diffused  by  the  same  central  sun  ;  that 

21 


242  CHEMISTRY  OF  ORGANIZATION. 

these  things  are  absolutely  unknown;  but  what  a  conception  do 
they  give,  of  that  inscrutable  agency  by  which  the  elements  are 
governed  ;  of  the  powers  of  that  Almighty  Mind  who  is  conversant 
with  them  all — by  whom  they  were  first  desigtied,  and  by  whom 
they  have  all  been  created  !  How  infinitely  must  His  knowledge 
surpass  whatever  we  can  imagine  :  how  far  is  His  power  beyond 
our  utmost  calculation  ! 

On  the  other  hand,  if  the  properties  of  the  elements  of  matter 
be  wonderful,  yet  more  wonderful  are  those  agents  within  orga- 
nized bodies,  by  which  they  are  directed.  With  the  intimate  na- 
ture indeed  of  these  agents  we  have  not  the  remotest  acquaintance, 
nor,  probably,  ever  shall  have.  But,  as  has  been  already  stated, 
we  can  trace,  to  a  certain  extent,  the  laws  of  action  which  these 
agents  obey  ;  we  observe  their  unvarying  adaptation  to  the  pro- 
perties of  carbon,  azote,  and  water,  on  which  they  chiefly  act; 
their  power,  within  certain  limits,  of  guiding  and  controlling  inor- 
ganic agents  ;  and  more  than  all,  that  mysterious  periodic  deve- 
lopement  and  decay,  which  every  organized  being  undergoes. 
These  facts  which  continually  present  themselves  to  our  notice, 
are  totally  inexplicable  according  to  those  laws  bv  which  inorganic 
bodies  are  governed  ;  and  are  referrible  only,  to  an  order  of  laws, 
which  the  Great  Author  of  Nature  has  not  chosen  to  reveal. 

Lastly,  we  cannot  close  this  chapter,  without  pointing  out  to 
the  reader  a  very  remarkable  contrast,  in  the  two  classes  of  objects 
which  have  engaged  our  attention.  The  number  and  diversity  of 
organic  agents  appear  to  be  endless  ;  in  the  creation,  therefore, 
of  these  agents,  the  Great  Author  of  Nature  has  chosen  to  mani- 
fest his  attribute  of  infinity.  But  in  the  creation  of  the  material 
elements  which  compose  the  frame  of  organized  beings,  He  has 
adopted  a  plan  directly  opposite.  Instead  of  different  principles; 
the  same  carbon,  the  same  azote,  the  same  water,  enter  into  every 
living  being,  from  the  lowest  plant  upward  to  man.  Amidst  the 
wonders  of  creation,  it  is  perhaps  difficult  to  say  what  is  most 
wonderful ;  but  we  have  often  thought,  that  the  Deity  has  displayed 
a  greater  stretch  of  power,  in  accommodating  to  such  an  extraor- 
dinary variety  of  changes,  a  material  so  unpromising  and  so  refrac- 

the  wliole  system  obeys  the  same  laws  ;  and  that  the  diflTcrent  planets  hi- 
fluencc,  and  are  influenced  by  each  other;  we  are  warranted  in  believing 
that  tlie  phinets  are  essentially  composed  of  the  same  elementary  princi- 
ples. But  admittinfj  that  the  heat  and  lii^ht  of  the  sun  are  distributtd  ac- 
cording- to  the  hiws  which  they  seem  universally  to  obey  ;  the  heat  in  Mer- 
cuiy,  close  to  tlie  sun,  and  tiie  cold  in  Saturn,  at  the  other  extreme,  must 
be  Hlikcso  intense,  that  org-anized  being-s,  such  as  inhabit  this  earth,  could 
not  exist  for  :i  moment.  In  the  different  planets,  therefoi-e,  may  not  the 
living  principle  be  attached  to  different  elements,  more  or  less  fixed  or 
volatile,  a3  tlie  distance  of  the  planet  from  the  sun  may  require  ? 


MODES  OF  NUTRITION.  243 

tory  as  charcoal,  and  in  finally  uniting  it  with  the  human  mind  ; 
llian  was  requisite  for  ifie  creation  of  the  human  mind  itself.  To 
Hin>,  however,  all  things  are  alike  easy  of  accomplishment ;  and 
He,  doubtless,  has  willed  these  and  other  proofs  of  His  omnipo- 
tence, in  order  to  convince  us  of  this  truth, — that  the  Creator  of 
the  mind,  could  alone  have  created  the  matter  with  which  the  mind 
is  associated  ! 


CHAPTER  H. 

OF  THE  MODES  OF  NUTRITION  ;  COMPREHENDING  A  SKETCH  OF  THE  ALI- 
MENTARY APPARATUS ;  AND  OF  ALIMENTARY  SUBSTANCES  IN  PLANTS, 
AND  IN  ANIMALS. 

The  subsistence  of  all  organized  beino;s  is  derived  from  sources 
external  to  themselves.  Their  means  of  subsistence,  however, 
as  well  as  the  modes  in  which  the  aliments  are  applied,  exhibit 
an  almost  endless  variety.  As  might  be  expected,  the  widest 
differences,  both  in  the  nature  of  the  alimentary  substances,  and 
in  the  manner  of  their  introduction,  are  between  plants  and  ani- 
mals. We  shall,  therefore,  consider  the  subject  of  nutrition  under 
these  two  heads. 


Section  I. 

Of  the  Modes  of  the  Nutrition  of  Plants  ;  and  of  the  Nature 
of  those  Matters  by  which  their  Nutrition  is  effected, 

A  MINUTE  investigation  of  the  anatomy  and  the  physiology  of 
plants  would  be  quite  foreign  to  the  object  of  this  treatise.  At 
the  same  time,  it  is  necessary  that  the  reader  should  have  some 
insight  into  these  departments  of  knowledge,  in  order  that  he  may 
be  enabled  to  understand  the  collateral  researches  which  it  is  our 
duty  to  illustrate. 

"  If  we  reflect  upon  the  phenomena  of  vegetation,"  says  Pro- 
fessor Lindley,  "our  minds  can  scarcely  fail  to  be  deeply  im- 
pressed with  admiration  at  the  perfect  simplicity,  and,  at  the 
same  time,  faultless  skill,  with  which  all  the  machinery  is  con- 
trived, upon  which  vegetable  life  depends.  A  few  forms  of  tissue 
interwoven  horizontally  and  perpendicularly  constitute  a  stem; 
the  developement,  by  the  first  shoot  that  the  seed  produces,  of 
buds  which  grow  upon  the  same  plan  as  the  first  shoot  itself, 
and  a  constant  succession  of  the  same  phenomenon,  causes  an 


244  CHEMISTRY  OF  ORGANIZATION. 

increase  in  t?ie  length  and  breadth  of  the  plant ;  an  expansion  of 
the  bark  into  a  leaf,  within  which  ramify  veins  proceeiHng  from 
the  seat  of  nutritive  matter  in  the  new  shoot,  the  provision  of  air 
passages  in  its  substance,  and  of  evaj)oraling  pores  on  its  surface, 
enables  the  crude  fluid  sent  from  the  roots  to  be  elaborated  and 
digested  until  it  becomes  the  peculiar  secretion  of  the  species  : 
the  contraction  of  the  branch  and  its  leaves  forms  a  fiower  ;  the 
disinteorration  of  tlie  internal  tissue  of  a  petal  forms  an  .  anther  ; 
the  folding  inwards  of  a  leaf  is  sufficient  to  constitute  apistillum  ; 
and  finally,  the  gorging  of  the  pistillum  with  fluid  which  it  can- 
not part  with,  causes  the  production  oC  afridt.''^* 

The  "crude  fluid  sent  up  from  the  roots"  of  plants,  or  their 
sap,  as  it  is  termed,  is  found  to  consist  of  water,  mucilage,  and 
sugar,  with  some  minute  portions  of  other  matters,  generally 
saline.  Though,  under  certain  circumstances,  moisture  be  ab- 
sorbed by  the  leaves  of  all  plants,  yet  there  is  no  doubt  that  a 
great  part  of  their  nourishment  enters  by  their  roots  ;  not,  how- 
ever, by  the  whole  root  indiscriminately  :  the  nourishment  of 
plants  is  taken  up  chiefly  by  the  minute  fibrous  parts  termed 
spongioles.  Hence,  these  minute  fibrous  parts  are  of  the  utmost 
importance  in  the  vegetable  economy,  and  ought  to  be  carefully 
preserved  in  transplantation,  otherwise  the  plant  will  certainly 
perish.  In  some  instances,  roots  appear  to  be  intended  to  act  as 
reservoirs  of  nourishment  for  the  support  of  the  plants  of  the 
succeeding  year,  on  their  first  developement.  There  are  such 
roots  in  liie  Orchis  and  Dahlia  tribes,  and  in  others.  Of  late  it 
seems  to  have  been  satisHictorily  establisheil,  that  the  roots  of  all 
plants,  besides  imbibing  nourishment,  perform  also  an  excretory 
office  ;  and  that  in  the  soil  in  which  plants  grow,  there  are  de- 
posited by  the  roots,  certain  matters  of  an  excrcmentitious  nature, 
injurious  to  the  plants  from  which  they  have  been  separated  ;  and 
which  therefore,  cannot  be  absorbed  again,  till  they  have  under- 
gone decomposition.  Such  excreted  matters  have  been  adduced 
as  the  reason,  why  a  soil  becomes  so  much  deteriorated  by  any 
one  species  of  plant  having  long  grown  in  it,  that  it  will  not  sup- 
port other  individuals  of  the  same  species  :  whence  the  necessity 
of  a  rotation  of  crops. 

The  principal  ingredient  in  the  sap  of  plants,  as  already  ob- 
served, is  water.  'JMie  quantity  of  sap  in  some  plants,  is  almost  in- 
credible ;  and  not  less  so,  is  the  force  with  which,  on  the  ap- 
proach of  warm  weather  in  our  climates,  and  at  the  commence- 
ment of  the  rainy  season  within  the  tropics,  that  sap  is  determined 
upwards.  The  general  composition  of  the  sap  varies  considerably 
in  diflerent  parts  of  the  same  plant.  For  instance,  sap  taken  from 

•   Introduction  to  Botany,  p.  216. 


NUTRITION  OF  PLANTS.  245 

the  roots  is  little  more  than  water ;  while  the  quantity  of  saccha- 
rine and  oiher  matters  contained  in  the  sap,  increases  in  its  pro- 
gress 'dUmg  the  stem  to  the  higher  parts  of  the  plant.  When  the  sap 
begins  to  rise,  the  leaves  at  the  same  time  begin  to  be  developed. 
From  the  leaves  principally  the  watery  portions  of  the  sap 
are  evaporated  ;  and  the  evaporation  is  copious  and  un<;easing. 
The  more  solid  matters  thus  remain  dissolved  iu  a  less  proportion 
of  water  ;  and  after  undergoing  further  changes,  as  is  supposed, 
in  the  leaves  chiefly,  these  matters  are  returned,  along  with  the 
remaining  water,  to  be  deposited  in  other  parts  of  the  plant,  for 
its  future  uses.  It  seems  now  to  be  generally  admitted,  that  one 
part  of  the  food  of  plants  is  the  matter  extracted  from  the  soil ; 
and  that  this  matter  is  taken  up  with  the  watery  portion  of  the  sap 
above  mentioned.  It  seems  also  to  be  admitted,  that  carbonic 
acid  gas  is  in  some  way  indispensable  to  vegetation  ;  "  for  it  has 
been  ascertained,  that  feed  plants  as  you  will,  they  will  neither 
grow  nor  live,  whether  you  offer  them  oxygen,  hydrogen,  azote, 
or  any  other  gaseous  or  fluid  principle,  unless  carbonic  acid  is 
present."  Like  the  other  nutritious  matters,  this  carbonic  acid 
is  partly  taken  up  by  the  roots  ;  but  under  certain  circumstances, 
it  is  also  separated  from  the  air,  and  absorbed  by  the  leaves.  The 
circumstances  under  which  this  absorption,  or  rather  decomposi- 
tion, of  carbonic  acid,  by  the  leaves  takes  place,  are  most  curious 
and  important.     They  are  understood  to  be  as  follows  : 

During  the  day,  and  particularly  during  sunshine,  the  leaves  of 
plants  have  the  power  of  abstracting  the  carbonic  acid  from  the 
atmosphere.  The  carbon  of  the  acid,  and  perhaps  also  a  little  of 
its  oxygen  combine  with  the  plant ;  while  the  greater  part  of  the 
oxygen  remains,  and  is  diffused  through  the  atmosphere  in  a 
gaseous  state.  During  the  night,  on  the  contrary,  or  in  the  shade, 
plants,  in  general,  convert  a  portion  of  the  oxygen  of  the  atmo- 
sphere into  carbonic  acid  ;  but  the  quantity  thus  converted,  is  less 
than  that  separated  from  the  carbonic  acid  which  they  decompose, 
under  the  influence  of  the  solar  light.  At  the  same  time  with 
this  formation  of  carbonic  acid  by  plants  during  the  night,  they 
are  said  also  to  absorb  from  the  atmosphere  a  certain  portion  of 
oxygen  ;  to  replace  that  which  had  been  given  off,  during  expo- 
sure to  sunshine,  on  the  preceding  day.  Plants  absorb  carbon  as 
long  as  they  are  exposed  to  the  light ;  during  the  season,  there- 
fore, when  the  day  is  long  and  the  night  is  short,  plants  give  off 
much  less  carbon  than  they  absorb.  This  excess  of  the  absorp- 
tion of  carbon,  is  probably  one  reason  why  in  the  Polar  latitudes, 
the  progress  of  vegetation  is  so  rapid.  By  a  beautiful  provision 
of  nature,  in  the  course  of  the  short  summer  of  a  few  weeks,  but 
of  unvarying  light,  plants,  in  these  latitudes,  go  through  all  the 
changes  which  in  hotter  climates  require  many  months. 

21  * 


246  CHEMISTRY  OF  ORGANIZATION. 

These  phenomena  of  gaseous  absorption  and  secretion  in  the 
leaves  of  phirits,  seem  to  be  produced  by  a  portion  of  the  leaf  pe- 
culiarly organized,  and  situated   immediately  under  its  external 
covering  or  epidermis.     Professor   Burnet  has  lately  explained 
these  phenomena,  by  referring  them  to  the  respiration  and  diges- 
tion of  plants.     The  process  of  respiration  in  plants,  is  supposed 
to  be  continual  ;    and  to  be  accompanied,  as   in  animals,  by  the 
formation  and  emission  of  carbonic  acid  gas.     While  digestion, 
whicli   consists  in  the  decomposition  of  carbonic  acid  gas,  takes 
place  only  during  the  exposure  of  plants  to  the  influence  of  the 
light — the  carbon  of  the  carbonic  acid  being  separated  from  the 
oxygen,  and  absorbed.     Hence  a  plant  exposed  to  sunshine  puri- 
fies the  air,  by  digesting  the  carbonic  acid,  the  carbon  of  which 
it  appropriates  ;    while  it  sets  the  oxygen  free.     In  the  dark,  on 
the   contrary,  digestion   ceases,   but  respiration  continues  ;    and 
carbonic  acid  gas  is  thus  accumulated  in  the  surrounding  atmo- 
sphere. 

With  respect  to  the  "  peculiar  principles  of  plants,"  these  are 
as  numerous  as  the  individual  plants  themselves  ;  so  that  to  at- 
tempt any  detailed  account  of  them  here,  would  be  quite  imprac- 
ticable. Generally  speaking,  the  peculiar  principles  found  in 
plants  may  be  divided  into  three  great  classes  : — those  vegetable 
principles  in  which  hydrogen  and  oxygen  are  combined  in  the 
proportions  that  form  water;  as  in  the  division  of  5acc/?r/rme 
bodies,  described  in  a  former  chapter  : — those  principles  in  which 
hydrogen,  or  rather  carbon  and  hydrogen,  predominate  ;  which 
gfucrally  have  more  or  less  of  an  oily  character ; — and  those 
principles  in  which  oxygen  predominates  ;  which  have  usually 
an  acid  character.  Besides  these  three  great  classes  of  vegetable 
principles,  there  are  some  that  contain  azote,  and  perhaps  other 
elements  ;  many  of  which  principles  also  exhibit  weak  alkaline 
powers  :  such  are  the  peculiar  principles  of  Opium  and  other 
Narcotics  ;  also  of  Cinchona  ;  and  a  variety  of  others,  chiefly 
eni ployed  as  Medicinal  agents. 


Section  II. 

Of  the  Modes  of  Nutrition  in  Animals  ;  and  of  the  Alimentary 
iSitO stances  by  which  they  are  nourished. 

To  beings,  like  animals,  endowed  with  locomotive  powers,  the 
absorption  of  their  nourishment  from  without,  would  have  been 
exceedingly  inconvenient.  Animals  have,  therefore,  been  fur- 
nished willi  an  additional  receptacle  and  apparatus  subservient  to 
nutrition,  into  which,  as  inclination  or  circumstances  may  prompt 


ORGANS  OF  DIGESTION  IN  ANIMALS.  247 

them,  their  food  is  conveyed  at  intervals  ;  and  from  which,  after 
havinof  undergone  certain  chano^es,  the  food  is  absorbed  and  dis- 
tribnted  over  their  system,  as  the  exigencies  of  that  system  may 
require.  Hence  the  distinction  between  plants  and  animals  ; — 
plants  absorb  their  nourishment  by  external,  animals  by  internal, 
roots  or  spongioles.  We  need  scarcely  remark,  that  the  stomach 
and  alimentary  canal,  with  their  appendages,  are  the  internal  ap- 
paratus to  which  we  ;illude  ;  and  that  this  internal  apparatus  con- 
stitutes a  marked  difference  between  plants  and  animals. 

1.  Of  the  Organs  of  Digestion  in  Animals. — Among  the  dif- 
ferent tribes  of  animals,  there  is  an  almost  endless  diversity  ia 
the  formation  of  the  alimentary  organs  ;  and  as  these  organs  vary, 
not  only  in  their  own  formation,  but  also  with  respect  to  the 
auxiliary  apparatus,  and  appendages  of  every  kind,  connected  with 
them  ;  any  detailed  account  of  the  alimentary  system  would  at 
present  be  quite  uncalled  for.  In  general,  the  alimentary  canal 
of  the  higher  classes  of  animals,  consists  of  a  tube  of  greater  or 
less  elongation  ;  expanded  in  some  parts  of  its  length  ;  terminated 
at  one  extremity  by  a  mouth,  into  which  the  food  is  received  ; 
and  at  the  other,  by  a  provision  for  the  removal  of  excrementi- 
tious  matters.  In  some  of  the  less  perfect  animals,  the  alimentary 
canal  has  only  one  aperture  ;  in  these  animals,  of  course,  instead 
of  a  canal,  there  is  a  kind  of  sac.  In  a  very  few  other  animals, 
the  alimentary  cavity  has  numerous  apertures.  In  all  instances, 
however,  and  whatever  may  be  the  nature  of  the  alimentary  mat- 
ters, these  matters,  after  having  been  retained  for  some  time  in 
the  organs  appropriated  to  nutrition,  are  reduced,  more  or  less,  to 
a  fluid  state — are  dtgested,  in  the  common  sense  of  the  term, 
and  are  converted  into  what  is  denominated  chyme.  The  more 
nutritious  parts  of  the  fluid  chyme,  or  the  chyle  as  they  are 
termed,  are  then  absorbed,  and  distributed  through  the  system  for 
the  reparation  of  the  animal;  while  the  insoluble  and  other  mat- 
ters, are  separated  as  excrementitious. 

We  have  already  alluded  to  the  endless  diversity  observable  in 
the  form  and  arrangements  of  the  alimentary  canal  in  the  different 
kinds  of  animals.  A  few  of  the  most  remarkable  of  these  diver- 
sities among  the  more  perfect  animals  will  be  noticed,  in  the  out- 
line we  are  now  to  give  of  the  alimentary  canal  as  existing  in  the 
human  body. 

Of  the  Mouth  and  its  Appendages. — "  In  no  apparatus  put 
together  by  art,"  says  Paley,  "  do  I  know  such  multifarious  uses 
so  aptly  contrived  as  in  the  natural  organization  of  the  human 
mouth."  "  In  this  small  cavity  we  have  teeth  of  different  shape, 
— first  for  cutting,  secondly  for  grinding  ;  muscles  most  artificially 
disposed  for  carrying  on  the  compound  motion  of  the  lower  jaw, 
half  lateral  and  half  vertical,  by  which  the  mill  is  worked ;  foun- 


248  CHEMISTRY  OF  ORGANIZATION. 

tains  of  saliva  sprinjrin^  np  in  different  parts  of  the  cavity  for  the 
nioi?:tening  of  the  food,  while  the  mastication  is  going  on  ;  glands 
to  Iced  the  fountains  ;  a  muscular  construction  of  a  very  peculiar 
kind  in  the  back  part  of  the  cavity,  for  the  guiding  of  the  pre- 
pared aliment  into  its  passage  towaids  the  stomach,  and  in  many 
cases  for  carrying  it  along  that  passage."  "In  the  meantime, 
and  within  the  same  cavity,  is  going  on  another  business  altoge- 
ther different  from  what  is  here  described — that  of  respiration 
and  of  speech.  In  addition,  therefore,  to  all  that  has  been  men- 
tioned, we  have  a  passage  opened  from  this  cavity  to  the  lungs, 
for  the  admission  of  air,  exclusively  of  every  other  substance  ;  we 
have  muscles,  some  in  the  larynx,  and  without  number  in  the 
tongue,  for  the  purpose  of  modulating  that  air  in  its  passage,  with 
a  variety,  a  compass,  and  a  precision  of  which  no  other  musical 
instrument  is  capable.  And  lastly,  we  have  a  specific  contrivance 
for  dividing  the  pneumatic  part  from  the  mechanical,  and  for  pre- 
veniitig:  one  set  of  actions  inlerferino^  with  the  other."  "The 
niouih,  with  all  these  intentions  to  serve,  is  a  single  cavity  ;  is 
one  machine,  with  its  parts  neither  crowded  nor  confined,  and 
each  unembarrassed  by  the  rest."'^  Such  is  Paley's  graphic  de- 
scription of  the  human  mouth  and  its  appendages:  we  have  quoted 
it  at  length,  that  it  may  serve  as  a  text  for  illustr-ation. 

Man  has  been  observed  to  differ  more  from  other  animals  in 
the  form  of  his  lower  jaw,  than  in  the  form  of  any  other  bone  of 
his  body.  Tiiis  difference  consists  chiefly  in  the  prominence  of 
the  cliin  ;  that  peculiar  characteristic  of  the  human  countenance, 
which  distinguishes  more  or  less  every  race  of  mankind,  and  is 
found  in  no  other  animal  whatever.  There  is  likewise  a  striking 
dilference,  among  the  various  tribes  of  animals,  in  the  mode  of 
articulation  of  the  lower  jaw  ;  which  in  all  cases  is  singularly 
adajilcd  to  the  nature  of  the  food  of  the  animal.  Thus,  in  the 
carnivor'ous  tribes,  the  artrcidalion  is  so  arranged  that  the  jaw  can 
move  only  up  and  down  ;  and  is  almost  entirely  incapable  of  that 
lateral  movement,  which  is  essential  to  genuine  mastication. 
Hence  such  animals  cut  and  tear  their  food,  and  swallow  it  in 
large  pieces.  But  those  animals  that  live  on  vegetables,  in  addi- 
tion to  the  vertical  motion  of  their  lower  jaw,  have  the  power  of 
moving  it  backwards  forwards,  or  to  either  side,  so  as  to  produce 
a  grinding  effect,  admirably  fitted  for  triturating  the  vegetable 
matters  on  which  they  subsist. 

-The  feefh  next  claim  our  attention,  as  being  not  less  suited  to 
the  hattits  of  the  animal,  than  in  the  form  of  the  jaw  in  which 
they  arc  set.  Teeth  arc  divided  by  naturalists  into  three  orders  : 
— The  hiciaorca,  or  culling  teelh,  placed  in  the  front  part  of  the 
mouth;  the  Cuspiduti^  canine,  or  corner  teeth,  usually  placed 

•  Natuiul  Theology',  chap.  ix. 


ORGANS  OF  DIGESTION  IN  ANIMALS.  249 

near  the  angles  of  the  jaw  ;  the  Molares,  grinding,  or  lateral  teeth, 
which  always  occupy  the  sides  and  back  part  of  the  jaw.  In 
man,  and  in  those  animals  which  most  nearly  resemble  him  in 
their  structure,  teeth  exist  of  all  the  above  varieties  of  form.  But 
many  species  want  one  or  other  of  these  varieties;  while  the  teeth 
they  possess,  are  of  a  form  and  size  very  unlike  the  same  teeth 
in  man.  I'hus,  in  animals  which  live  chiefly  on  the  harder  ve- 
getable substances,  and  which,  from  their  peculiar  mode  of  feed- 
ing, have  been  termed  gnawing  animals,  the.  incisor  teeth  are 
the  most  remarkably  developed  ;  as  these  teeth  are  the  best 
adapted,  and  indeed  are  the  most  necessary,  to  their  habits. 
In  carnivorous  animals,  on  the  other  hand,  the  canine  teeth  are 
of  chief  importance  ;  as  enabling  these  animals  to  seize  and  hold 
their  prey:  in  such  animals,  accordingly,  the  canine  teeth  are  the 
most  perfectly  formed.  LasUy,  in  the  animals  that  feed  on  grass, 
and  other  herbaceous  substances,  and  whose  aliments  require  long 
and  complete  mastication,  the  Molares,  or  grinding  teeth,  attain 
the  greatest  enlargement;  and  in  many  of  these  animals  the  inci- 
sor and  the  canine  teeth  are  entirely  wanting.  Besides  the  adapta- 
tion of  the  form,  the  enamel  or  harder  cutting  portion  of  the  teeth, 
is  distributed  over  and  throughout  their  texture,  according  to 
their  intended  uses,  in  a  manner  that  is  truly  extraordinary.  The 
description  however  of  the  arrangement  of  the  enamel,  as  well 
indeed  as  a  minute  account  of  the  teeth  themselves,  belongr  to  the 
physiologist,  on  whose  province  we  shall  not  further  intrude. 
But  it  is  impossible  to  take  even  the  most  superficial  view  of  the 
teeth  of  animals,  without  being  struck  with  the  admirable  design 
and  fitness  they  display,  throughout  their  whole  fabrication. 

The  next  auxiliary  appendages  of  the  mouth  are  the  glands 
that  secrete  the  saliva;  in  which  we  observe  the  same  beautiful 
arrangement  as  in  the  form  and  structure  of  the  teeth.  In  man, 
though  the  apparatus  for  the  secretion  of  ih.e  saliva,  is  by  no  means 
of  large  size,  yet  the  quantity  of  fluid  whicii  the  salivary  glands 
are  capabla  of  secreting,  and  do  secrete  during  mastication,  is 
very  considerable  ;  often  amounting,  it  is  said,  to  half  a  pint  or 
more.  This  fluid,  in  its  perfectly  healthy  state,  is  neither  acid 
nor  alkaline,  or  alkaline  only  in  a  slight  degree  ;  but  occasionally 
it  assumes  an  acid  character.  Besides  the  great  utility  of  the 
saliva  in  moistening  the  food,  we  cannot  doubt  that  it  assists,  and 
is  even  necessary  to  the  full  completion  of  the  succeeding  di- 
gestive process.  By  a  beautiful  arrangement,  those  animals 
that  do  not  masticate  their  food,  as  the  carnivorous  tribes,  have 
very  small  salivary  glands  ;  while  in  animals  whose  food  requires 
long  mastication,  as  in  ruminating  animals — the  cow  and  the 
sheep,  for  example,  the  salivary  glands  are  very  large. 

The  passage  by  which  the  masticated  food  is  conveyed  from 
the  mouth  to  the  stomach  is  termed  the  oesophagus.     Like  the 


250  CHEMISTRY  OF  ORGANIZATION. 

wliole  frame,  the  CEsopbagus  is  admirably  adapted  for  its  office  ; 
and  in  (btfcrent  animals,  varies  in  size  and  structure,  according 
to  their  habits.  These  differences,  however,  scarcely  concern  us  at 
present,  and  we  pass  on  to  that  important  organ — the  Stomach. 

The  human  stomach  is  a  membranous  bag,  of  a  shape  rather 
difficult  to  be  de.-cribed,  so  as  to  convey  a  clear  notion  of  it  to  the 
reader.  If  we  imagine  two  cones  united  at  their  bases,  and  the 
figure  thus  produced  to  be  bent  into  a  semicircular  form,  some 
idea  may  be  obtained  of  ihe  outline  of  the  stomach  in  the  human 
species.  In  respect  to  its  size,  the  human  stomach  varies  :  but 
in  the  adult,  its  capacity  is  usually  such  as  to  contain  about  two 
or  three  pints.  The  stomach  is  situated  immediately  under  the 
diaphragm;  but  the  precise  place  of  the  organ  differs  somewhat 
with  its  state  of  repletion.  The  general  position  of  the  stomach 
is  transverse,  or  horizontal,  supposing  the  body  to  be  upright  ; 
the  left  orifice,  or  cardla,  which  communicates  with  the  oeso- 
phajjus,  being  somcwh;!t  higher  than  the  right  orifice,  ihe  pylorus y 
through  which  the  food  is  transmitted  to  the  further  portion  of 
the  alimentary  canal.  The  upper  space  between  the  two  ori- 
fices is  usually  termed  the  small  curvature  ;  the  lower  space,  the 
great  curvature,  of  the  stomach.  Numerous  glands  occupy  the 
internal  surface  of  the  stomaf^h,  particularly  near  its  pyloric  ori- 
fice. By  these  glands  a  fluid  is  secreted  of  the  highest  import- 
ance in  the  diofesiive  functions,  on  the  nature  of  which  we  shall 
eidargpi  hereafter. 

Such  is  the  stomach  of  man  ;  but  the  form  and  the  magnitude 
of  this  organ  vary  almost  infinitely  in  different  animals,  according 
to  the  nature  of  their  food,  and  other  circumstances.  We  can, 
at  present,  notice  only  two  or  three  of  the  most  remarkable  di- 
versities. In  most  carnivorous  animals,  the  stomach  bears  a  re- 
semblance to  that  of  man.  There  is  also  a  resemblance,  at  least 
externally,  in  certain  herbivorous  animals  ;  as  in  the  horse,  the 
rabbii,  and  others.  The  internal  arrangements,  however,  are 
diHerenl ;  thus,  in  the  animals  al)0ve  mentioned,  the  left  or  cardiac 
half  of  the  stomach  is  lined  with  cuticle;  while  the  other  half, 
towards  the  pylorus,  has  the  usual  villous  and  secreting  surface. 
Hence,  these  two  portions  of  the  stomach  perform  very  different 
offures,  and  generally  contain  food  in  very  different  states  of  re- 
dutrtion.  Tlie  most  complicated  and  artificial  arrangement,  how- 
ev(!r,  both  with  respect  to  the  structure  of  the  parts,  and  the  lining 
meuibrancs,  h  found  in  the  well-known  four  stomachs  of  the  ani- 
mals that  ruminate  and  have  divided  hoofs  ;  as  the  cow  and  the  sheep. 
We  shall  endeavour  to  give  a  general  description  of  these  four  sto- 
machs. The  first  stomarh  is  denominated  the  Paunch,  and  in 
the  adult  animal  is  by  far  the  laro-est.  The  second  stomach  fol- 
lows,  and  may  be  regarded  as  a  globular  appendage  to  the  paunch; 


ORGANS  OF  DIGESTION  IN  ANIMALS.  251 

from  which  it  is  distinguished,  principally,  by  the  regular  and 
beautiful  distribulion  of  its    internal    membrane    into    polygonal 
cells.     The  third  stomach  is  the  smallest  of  the  four,  and  is  the 
most  remarkable  in  its  structure  :   its  capacity  is  much  diminished 
by  numerous  and  broad  duplicatures  of  its  internal    membrane, 
which   are   placed  lengthwise,  and  vary  in   breadth   in   a  regular 
order.     The  fourth  stomach  is  next  in  size  to  the  paunch,  and  is 
lined  with  a  villous  membrane  approaching  to  that  of  the  human 
stomach,  which  this  fourth  stomach  may  be  supposed   to  repre- 
sent ;  the  three  preceding  stomachs  having  been  evidently  intended 
to  prepare  the  refractory  food  of  the  animal  for  the  true  digestive 
pro(:ess,  which  it  undergoes  in  this  last  stomach.     Every  one  is 
acquainted  with  the  fact  that  animals  furnished  with   the  gastric 
arrangements  above  described,  ruminate;  that  is  to  say,   have 
the  faculty  of  masticating  a  second  time,  and  at  their  leisure,  that 
food  which   had  been   hastily  swallowed,  and  deposited  in   their 
first  stomach.     The  contrivance  by  which   rumination  is  effected 
is  very  beautiful  ;  and  is  connected  vi^ith  the  peculiar  arrangement 
already  mentioned  of  the  four  stomachs,  with  respect  to  the  osso- 
phagus  :   but,   as   it  would  not  be  easy  in  a  few  words,   to   give 
more  than  a  general  outline  ;   we  must  refer  the  reader  to  anato- 
mical works,  for  a  more  particular  description  of  the  stomachs  of 
ruminating  asiimals.     The  only  other  modification  of  the  stomach 
which  we  shall  notice,  is  that  which  exists  in  some  birds  ;  as  for 
example,  in  the  common  fowl.     The  common  domestic  fowl,  as 
well  as  many  similar  birds,  has  a  sort  of  preliminary  stomach, 
termed  the  crop,  formed  by  an  expansion  of  the  oesophagus.     In 
the  crop,  the  hard  seeds,  and  other  compact  substances  which 
birds  devour,  are   macerated   and  s(»ftened,  and  perhaps  undergo 
further  changes,  before  they  enter  the  proper  stomach,  to  be  next 
considered.     The  proper  stomach,  or  gizzard,  of  birds,  is  a  hol- 
low muscle  of  great  strength,  lined  with  a  firm  and  thick  epider- 
mis, disposed  in  rugae,  and  admirably  adapted  for  triturating  the 
hard  matters  that  constitute  their  food.     The  small  stones  which 
these  birds  constantly  swallow  seem  also  to  promote  this  tritura- 
tion. 

We  have  given  the  above  short  sketch  of  the  structure  of  the 
stomachs  of  animals,  not  only  that  we  might  impart  to  the  general 
reader  a  faint  conception  of  the  extraordinary  design  manifested 
in  that  structure  ;  but  to  enable  us  to  show  the  object  of  diversity 
of  structure,  when  we  come  to  speak  of  the  function  of  digestion 
a  little  more  in  detail. 

Alter  the  stomach  we  proceed  to  the  consideration  of  the 
Intestinal  Canal.  In  man,  and  in  the  more  perfect  animals,  this 
canal  assumes  two  well  marked  forms,  usually  termed,  from  their 
relative  size,  the  small  and  the  large  intestines.     In  most  animals 


252  CHEMISTRY  OF  ORGANIZATION. 

resembling  man,  the  small  intestines  are  the  longest,  and  their  in- 
ternal snr(\ioe  is  villous.  The  coats  of  the  large  intestines  are 
thicker,  and  the  membrane  with  which  they  are  lined  is  very  rare- 
ly villous.  The  first  portion  of  the  small  intestines,  from  its 
supposed  length  termed  the  duodenum,  or  twelve-inch  intestine, 
begins  from  the  pyloric  orifice  of  the  stomach ;  and,  in  many 
animals  has  a  course  not  easy  to  be  described,  so  as  to  be  intelli- 
gible to  the  general  reader.  The  duodenum  terminates  in  the 
second  portion  of  the  small  intestines,  called  the  jejunum,  from 
its  being  usually  empty.  The  duodenum  differs  from  the  sto- 
mach and  other  parts  of  the  canal,  in  being  secured  in  its  position 
by  various  attachments  ;  while  the  stomach  and  other  parts  of 
the  canal,  are  comparatively  loose  and  floating.  This  fixedness 
appears  to  serve  many  wise  purposes,  on  which  we  cannot  dwell 
here;  but  one  purpose  probably  is,  to  ensure  the  easy  and  regu- 
lar passage  of  the  bile  and  the  pancreatic  fluids  into  this  part  of 
the  canal.  As  the  organs  producing  these  important  fluids  are 
fixed,  the  conducting  tubes  necessarily  require  also  to  be  con- 
nected with  a  fixed  organ  ;  otherwise  the  passage  of  the  fluids 
from  the  secreting  organs  to  the  intestine,  would  be  constantly 
liable  to  interruption.  The  duodenum  is  very  highly  organized, 
and  its  functions  are  probably  not  less  important  than  even 
those  of  the  stomach.  The  remainder  of  the  small  intestines 
is  divided  into  the  jejioiwn  already  mentioned,  and  the  ilimn; 
but  the  precise  place  where  one  ends,  and  the  other  begins,  is 
scarcely  definable  ;  nor  are  the  differences  of  structure  between 
the  two  so  obvious,  as  to  require   to  be  noticed  in  this  place. 

The  large  intestines  exceed  the  small  intestines  in  diameter, 
but  are  considerably  shorter  :  their  form  and  structure  are  also 
different.  The  first  division  of  this  portion  of  the  alimentary 
canal  is  termed  the  crecum ;  and,  in  man  at  lenst,  may  be  con- 
sidered as  little  more  than  the  head  or  commencement  of  the  next 
division-of  the  large  intestines,  termed  the  colon.  The  colon  is  of 
much  greater  diameter  than  any  other  part  of  the  intestinal  canal, 
and  constitutes  almost  the  entire  length  of  the  large  intestines. 
The  colon  begins  low  down  on  the  right  side  of  the  abdomen, 
then  ascending  to  the  level  of  the  stomach,  passes  across  to  the 
left  side,  immediately  below  that  organ.  On  the  left  side,  the 
colon  descends  again,  and  at  the  same  time  forms  what  is  called 
the  sigmoid  flexure.  The  colon  and  the  alimentary  canal  at 
length  terminate  in  what  is  named  the  rectum.  The  texture  of 
the  colon  is  much  thicker  than  that  of  any  other  portion  of  the 
canal.  Its  organization  also  is  peculiar ;  and,  like  the  whole  ar- 
rangement, wonderfully  adapted  for  the  purposes  which  this  por- 
tion of  the  c;uial  is  sujiposed  to  serve  in  the  animal  economy. 

Such  is  the  short  account  of  the  alimentary  canal  in  man.    We 


ORGANS  OF  PIGESTION  IN  ANIMALS.  253 

shall  now  state  some  of  the  more  remarkable  diversities  that  are 
observed  in  the  lower  animals. 

One  of  the  most  striking  circumstances  relative  to  the  alimen- 
tary canal  in  animals,  is  its  various  lengths  in  the  different  classes. 
In  man,  and  other  omnivorous  animals,  the  proportion  is  inter- 
mediate between  that  of  carnivorous  animals  on  the  one  hand, 
and  herbivorous  animals  on  the  other.  In  man,  the  whole  length 
of  the  canal  is  about  six  or  seven  times  that  of  the  body  ;  while 
in  carnivorous  animals  it  is  only  from  about  three  to  five  times 
that  length ;  and  in  graminivorous  animals,  as  in  the  sheep,  the 
length  of  the  canal  is  twenty-seven  times  that  of  the  body.  In 
other  herbivorous  animals,  the  length  of  the  canal  varies  from 
twelve  to  sixteen  times  that  of  the  body.  In  most  birds  the  ali- 
mentary canal  is  much  shorter  than  in  quadrupeds ;  the  length 
in  general,  being  between  twice  and  five  times  that  of  their  bodies  : 
while  in  many  reptiles  and  fish,  the  length  of  the  canal  scarcely 
exceeds  that  of  the  body  :  in  some  fish  it  is  even  less  ;  as  for 
example,  in  the  shark.  There  are  animals  that  feed  on  vege- 
tables, the  length  of  whose  alimentary  canal  is  not  so  great,  as 
in  the  instance  above  stated  ;  the  deficiency  in  length  being  ap- 
parently made  up  in  breadth.  Thus,  in  the  horse,  the  stomach 
is  simple,  and  not  much  developed,  when  compared  with  the 
size  of  the  animal  ;  nor  are  the  intestines  very  remarkable  for 
their  length ;  but  the  ccecum  and  the  large  intestines  are  enor- 
mously expanded  in  diameter.  The  coecum  of  the  horse  seems 
to  perform  many  of  the  ofl[ices  of  a  second  stomach,  and  is  of 
fully  equal  capacity.  There  are  in  animals,  many  other  beautiful 
arrangements  of  the  digestive  organs,  which  we  shall  pass  with- 
out further  notice  ;  as  our  desire  is  to  inform  the  reader  of  the 
general  connection  and  adaptation,  which  exists  between  the 
structure  of  animals,  and  the  food  on  which  they  live.  It  re- 
mains to  conclude  this  outline  of  the  digestive  organs,  with  a  few 
remarks  on  those  almost  invariable  accompaniments  of  the  ali- 
mentary canal, — the  liver ^  the  pancreas,  and  the  spleen. 

The  liver  is  the  largest  glandular  apparatus  in  the  body,  and 
one  of  its  important  ofiices  is  to  secrete  the  Bile;  which  secre- 
tion, as  before  observed,  enters  the  intestines,  near  the  commence- 
ment of  the  duodenum.  The  general  situation  of  the  human 
liver,  is  in  the  upper  part  of  the  abdomen,  under  the  ribs  on  the 
right  side;  from  whence  it. extends  more  or  less  to  the  region  of 
the  stomach,  and  in  some  instances,  even  to  the  left  side.  The 
appearance  and  form  of  the  liver,  are  too  well  known  to  require 
description  here ;  while  to  those  who  are  unacquainted  with 
these  particulars,  they  cannot  be  adequately  made  known  by 
words.  In  man,  and  the  greater  number  of  animals,  the  bile  is 
collected  in  a  small  bag,  termed  from  its  office,  the  gall-bladder. 

22 


254  CHEMISTRY  OF  ORGANIZATIOX. 

The  animals  wanting  a  gall-bladder  are  chiefly  vegetable  feeders  ; 
as  the  horse  and  the  goat  among  quadrupeds,  the  pigeon  and  the 
parrot  among  birds.  On  the  contrary,  most  amphibia  have  a  gall- 
bladder ;  but  it  exists  in  few  animals  lower  in  the  zoological 
scale.  The  liver  assumes  a  variety  of  forms  in  different  animals. 
In  many,  and  particularly  in  carnivorous,  animals,  the  liver  is 
more  divided  than  in  man  :  while  in  ruminating  animals, ^also  in 
the  horse,  the  hog,  and  others,  its  divisions  are  not  more  nume- 
rous than  in  man.  The  liver  of  birds  consists  of  two  lobes  of 
equal  size. 

The  pancreas,  or  sweetbread,  is  a  large  gland,  which,  in  the 
Iiuman  body,  lies  across  the  upper  and  back  part  of  the  abdomen, 
behind  the  stomach  ;  and  between  the  liver  and  the  spleen.  The 
pancreas  is  composed  of  numerous  small  glands,  whose  ducts 
unite  and  form  the  pancreatic  duct.  In  man  the  pancreatic  duct 
joins  tlie  gall  duct,  at  its  entrance  into  the  duodenum,  and  thus 
tlie  peculiar  secretion  of  the  pancreas  is  poured  into  that  intestine, 
commingled  with  the  bile.  In  animals  the  pancreas,  like  the 
liver,  is  much  varied  in  its  form  ;  and  its  duct,  instead  of  entering 
with  the  biliary  duct,  often  ,oins  the  intestinal  canal  separately  ; 
as  in  the  hare  and  others.  In  fishes  the  pancreas  is  wanting  ; 
but  what  are  termed  tiie  coscal  appendages,  are  supposed  to  have 
a  similar  office.  The  nature  of  the  pancreatic  fluid  will  be  con- 
sidered presently. 

The  spleen  in  man  is  situated  in  the  upper  and  left  side  of 
the  abdomen.  Its  shape  is  oblong,  and  its  colour  a  deep  mul- 
berry ;  more  nearly  resembling  that  of  the  liver  than  of  any  other 
organ.  The  spleen  has  no  excretory  duct,  and  its  use  is  very 
little  understood.  Among  the  less  perfect  animals,  the  spleen  is 
much  smaller  than  in  those  whose  structure  resembles  that  of 
man  :  and  where  there  is  more  than  one  stomach,  the  spleen  is 
always  attached  to  the  first.  The  situation  also  of  the  spleen 
varies  in  the  less  perfect  animals  ;  thus  in  the  frog,  it  is  fixed  in 
the  mesentery. 

We  proceed  to  notice,  very  briefly,  the  peculiar  circulation  of 
the  blood  in  the  abdominal  viscera  ;   together  with  the  character 
and  agency  of  that  portion  of  the  nervous  system,  which  is  con 
nected  with  the  digestive  and  assimilating  functions  of  animals. 

In  the  general  circulation  of  the  blood  through  an  animal  body  ; 
a  large  tube  or  artery,  communicating  with  the  heart,  is  gradually 
subdivided  as  it  is  prolonged  from  that  organ,  till  its  subdivisions 
finally  become  imperceptible.  While  in  this  state  of  minute  sub- 
division, the  arteries  assume  the  character  of  veins.  The  change 
the  veins  undergo  in  their  progress,  is  the  reverse  of  that  of  the 
arteries.  They  unite  gradually,  and,  at  lengtii,  form  one  or  two 
principal  tubes,  which  proceed  to  the  side  of  the  heart  opposite 


ORGANS  OF  DIGESTION  IN  ANIMALS.  255 

to  that  from  which  the  artery  originated.  Such  is  the  circulation 
of  the  blood  through  the  body  generally  ;  the  circulation  through 
the  lungs  is  merely  a  repetition  of  the  same  ariangement. 
Throughout  the  body,  therefore,  the  general  motion  of  the  blood 
in  arteries  is  from  greater  to  smaller  tubes  ;  while  in  the  veins  it 
is  from  smaller  to  greater  tubes.  By  a  beautiful  provision,  the 
veins  are  also  furnished  with  valves,  which  most  effectually  pre- 
vent the  regurgitation  of  the  blood :  without  such  valves,  the 
blood  could  scarcely  flow  in  a  regular  stream.  We  have  intro- 
duced these  remarks,  with  the  view  of  stating,  that  the  circulation 
of  the  blood  through  the  organs  of  digestion,  presents  a  remark- 
able exception  to  the  general  circulation  of  the  body.  Tiie  venous 
blood,  from  these  organs,  undergoes  a  preliminary  arterializing 
process  in  the  liver,  before  it  is  remingled  with  the  venous  blood 
from  the  rest  of  the  body.  That  is  to  say,  the  veins  from  the 
organs  of  digestion,  unite  into  one  large  vessel  termed  the  vena 
"portab  ;  which,  entering  the  liver,  is  ihere  again  subdivided,  in 
the  same  manner  as  an  artery.  These  ultimate  subdivisions  of 
the  vena  portse,  together  with  the  similar  subdivisions  of  the 
proper  artery  of  the  liver,  coalesce  ;  and  from  the  blood  tlius 
mixed  the  bile  is  separated.  The  coalesced  blood-vessels  assum- 
ing the  character  of  veins,  then  gradually  unite,  and  at  length  form 
two  or  three  large  tubes,  which  empty  themselves  into  the  general 
veins  going  to  the  heart ;  while  the  hepatic  ducts,  uniting  in  like 
manner,  convey  the  bile  to  the  gall-bladder.  Such  are  the  prin- 
cipal facts  connected  with  the  circulation  of  the  blood  in  the  abdo- 
minal viscera,  and  with  the  secretion  of  the  bile.  We  shall  soon 
have  occasion  to  bring  them  to  the  recollection  of  the  reader. 

When  speaking  of  organic  agents,  we  noticed  the  probability 
of  the  opinion,  that  in  living  beings,  there  exists  a  series  of  agen- 
cies gradually  raised  one  above  another  ;  each  agency  having 
more  or  less  control  over  all  those  below  it.  Now,  in  the  diges- 
tive and  assimilating  functions,  we  appear  to  have,  as  we  might 
expect,  the  lowest  of  tliese  agencies.  The  agencies  operating 
in  digestion,  and  in  the  first  stages  of  assimilation  are,  in  man, 
perhaps  the  same  that  exist  in  all  organized  beings,  vegetable 
as  well  as  animal;  and  are  only  a  few  degrees,  as  it  were, 
above  the  agencies  of  mere  inorganic  matter.  This  resem- 
blance is  inferred  from  the  phenomena  of  assimilation  ;  not  less 
than  from  the  peculiar  character  of  the  nerves,  distributed  over 
the  digestive  organs  ;  the  effects  of  which  nerves,  as  we  shall 
presendy  endeavour  to  show,  approach  more  nearly  to  those  of 
common  chemical  agents,  than  to  the  effects  of  any  agent  belong- 
ing to  the  animal  economy.  These  nerves  compose  what,  from 
their  peculiar  structure,  rre  termed  the  ganglionic  nerves.  In 
animals  of  the  very  lowest  kind,  the  ganglionic  nerves  alone  ap- 


256  CHEMISTRY  OF  ORGANIZATION. 

pear  to  exist ;  and  though  in  the  more  perfect  animals,  these 
nerves  are  connected  with  others  of  a  higher  character,  they 
always  form,  by  themselves,  a  peculiar  system  ;  the  functions  of 
which  seem  to  be  of  the  subordinate  character  above  noticed. 

2.  Of  Jilimentary  Substances. — It  may  be  considered  as  a 
general  rule,  that  organized  beings  adopt,  as  aliments,  substances 
lower  than  themselves  in  the  scale  of  organization  ;  or  which,  if 
not  originally  lower,  in  some  measure  become  so,  by  certain 
spontaneous  changes  they  undergo.  There  are,  of  course,  innu- 
merable exceptions  to  this  rule  ;  but  viewing  the  whole  of  ani- 
mated beings,  it  seems  to  be  a  law  of  nature.  Thus  plants,  and 
perhaps  the  very  lowest  kinds  of  animals,  have  the  power  of  assi- 
milating carbonic  acid  gas  :  the  powers  of  assimilation  of  plants, 
and  of  such  animals,  may  also  extend  to  other  inorganic  com- 
pounds of  carbon — indeed  they  seem  to  derive  their  chief  nou- 
rishment from  matters  of  that  nature.  Higher  in  the  zoological 
scale,  we  find  that  animals  almost  invariably  prey  on  those  that 
are  inferior  to  themselves,  either  in  magnitude,  in  organization, 
or  in  intelligence;  till  we  arrive  at  man  himself.  He,  as  his 
necessities,  or  as  his  fancies  may  dictate,  appropriates  every  nou- 
rishing substance,  even  carbonic  acid  gas  ;  which  his  stomach, 
perhaps  in  common  with  that  of  all  animals,  seems  to  have  the 
power  of  assimilating.  Of  course  a  lion,  or  even  a  crab,  can 
feed  on  the  body  of  a  man,  as  well  as  on  that  of  an  ox  or  of  an 
insect.  But  no  one,  we  presume,  will  assert,  that  man  is  the 
natural  prey  or  food  of  these  animals  ;  and  that  alone  is  the  de- 
gree of  immunity,  for  which  we  here  contend  :  for  in  all  the 
operations  of  nature,  we  must  try  to  discover  and  bear  in  mind, 
not  the  exception,  but  the  rule  ;  otherwise  we  shall  be  constantly 
liable  to  error. 

By  this  beautiful  arrangement  in  the  mode  of  their  nutrition, 
the  more  perfect  animals  are  exonerated  from  the  toil  of  the  initial 
assimilation  of  the  materials  composing  their  frame;  as  in  their 
food,  the  elements  are  already  in  tiie  order  which  is  adapted  for 
their  purpose.  Hence  the  assimilating  organs  do  not  require  that 
complication,  which  they  otherwise  would  have  needed ;  and 
much  elaborate  organization  is  saved.  Striking  illustrations  of 
this  abridgement  of  organization,  are  afTordcd  by  the  differences 
before  mentioned,  between  the  assimilating  apparatus  of  carnivo- 
rous and  of  graminivorous  animals.  According  to  the  scale 
which  this  difference  exhibits,  we  can  form  some  conception  of 
the  complication  that  would  be  requisite,  if  such  an  animal  as 
man  were,  like  a  plant,  destined  to  feed  on  carbonic  acid  gas  ;  or 
carburelted  hydrogen;  or  on  any  other  simple  compound  of 
carbon. 

Another  great  purpose  is  efTected  by  this  arrangement,  without 


FOOD  OF  ANI3IALS.  257 

which,  organization,  at  least  as  at  present  constituted,  could 
hardly  exist.  If  organized  beings  did  not  prey  on  each  other, 
their  remains  would,  in  time,  accumulate  in  such  quantity,  as  to 
he  nearly  incompatible  with  life  ;  certainly  with  animal  life  in  its 
most  perfect  condition,  as  it  is  at  present  known  to  us.  But  by 
the  arrangement  that  animals  are  food  to  each  other,  not  only  is 
an  opportunity  afforded,  for  the  existence  of  a  greater  number  of 
animals,  and  of  a  greater  variety  among  them  ;  but  the  obtrusion 
of  the  bodies  of  animals,  in  whom  life  has  become  extinct,  is 
entirely  prevented  :  nor,  is  the  removal  of  the  dead  animal  matter 
the  only  good  accomplished,  but  many  other  important  results  are 
obtained.  To  enter  upon  the  consideration  of  these,  would  be  fo- 
reign to  our  present  object:  there  is,  however,  one  consequence  of 
this  system  of  universal  voracity,  which  more  immediately  con- 
cerns us,  since  it  is  of  a  nature  so  comprehensive,  as  to  suggest 
a  natural  classification  of  alimentary  substances  ;  we  allude  to 
the  similarity  of  composition  among  the  staminal  principles  which 
constitute  the  fabric  of  organized  beings. 

T  • 

In  our  introductory  remarks  on  the  chemistry  of  organization, 
we  showed  that  organized  matters,  however  apparently  dissimilar, 
yet,  chemically  speaking,  are  often  nearly  related.  Of  this  rela- 
tion we  gave  as  an  example,  the  composition  of  the  extensive 
class  of  substances,  denominated  the  saccharine  group  ;  all  of 
which,  notwithstanding  the  endless  diversity  of  their  appearance, 
we  showed  to  be  essentially  alike  in  their  composition,  and  to 
consist  of  carbon  associated  with  water.  Saccharine  substances 
are  chiefly  found  in  the  vegetable  kingdom,  of  which  they  form 
the  characteristic  staminal  principle. 

Another  well  known  class  of  bodies,  existing  both  in  vegetables 
and  in  animals,  are  those  whose  character  is  oily.  Oleaginous 
bodies  occur  in  an  infinite  variety  of  forms,  some  being  solid, 
others  fluid  ;  yet,  in  every  instance,  their  peculiar  properties  are 
so  strongly  marked,  that  we  seldom  hesitate  about  their  nature. 
In  this  distinctness  of  outward  appearance,  oily  bodies  are  strong- 
ly contrasted  with  the  saccharine  group  before  mentioned  ;  many 
of  which  have  few  apparent  and  sensible  properties  in  common. 
The  composition  of  all  the  bodies  of  this  oleaginous  group,  which 
we  have  hitherto  had  an  opportunity  of  examining  in  a  satisfac- 
tory manner,  we  have  found  to  be  essentially  the  same  :  they  are 
either  composed  of  olefiant  gas  and  water,  or  have  a  reference  to 
that  composition.  Such  is  also  the  composition  of  the  well  known 
proximate  principle  termed  spirit  ofwine^  or  alcohol ;  into  which, 
most  substances  belonging  to  the  saccharine  group,  under  favour- 
able circumstances,  are  readily  convertible  by  the  process  termed 
fermentation. 

When  almost  any  part  of  an  animal  body,  (with  the  exception 

22  * 


258  CHEMISTRY  OF  ORGANIZATION. 

perhaps  of  those  matters  of  a  purely  oleaginous  character)  is  boiled 
in  water,  it  is  separated  into  two  portions, — one  soluble  in  water, 
and  lorminiT  with  the  water  a  tremulous  jelly,  or  gelatine — the 
other  remaining  insoluble,  indeed  becoming  harder,  the  longer  it 
is  boiled  ;  and  which,  from  the  identity  of  its  properties  to  those 
of  the  white  of  an  egg^  is  denominated  albumen.  These  animal 
principles  exist  in  very  different  proportions  in  the  difierent  tex- 
tures ;  some  of  these  textures,  as  the  skin,  being  convertible  al- 
most entirely  into  gelatine  ;  while  others  yield  comparatively  little 
gelatine,  and  consist  principally  of  albumen.  In  no  animal  com- 
pound does  gelatine  exist  as  a  fluid ;  hence,  it  has  been  supposed 
to  be  produced  by  boiling;  but  the  supposition  does  not  appear  to 
be  well  founded.  One  of  the  most  remarkable  properties  of  gela- 
tine, is,  its  ready  convertibility  into  a  sort  of  sugar,  by  a  process 
similar  to  that  by  which  starch  may  be  so  converted.  Gelatine 
may  be  considered  as  the  least  perfect  kind  of  albuminous  matter 
existing  in  animal  bodies  ;  intermediate,  as  it  were,  betw^een  the 
saccharine  principle  of  plants,  and  thoroughly  developed  albu- 
men :  indeed,  gelatine  in  animals,  may  be  said  to  be  the  counter- 
part of  the  saccharine  principle  in  vegetables.  Albumen  exists  in 
the  fluid  state  as  a  component  of  the  blood :  small  quantities  of  fluid 
albumen  are  also  contained  in  certain  animal  secretions  :  but  there 
is  much  more  of  the  principle  in  a  solid  state  ;  forming  what  is 
termed  coagulated  albumen.  The  blood  likewise  contains  Fibrin, 
another  modification  of  the  albuminous  principle,  in  a  fluid,  or  at 
least  in  a  suspended  state:  though  the  most  frequent  condition  of 
Fibrin,  is  that  of  a  tough  fibrous  mass,  in  which  condition,  toge- 
ther with  all)umen,  it  forms  the  basis  of  the  muscular  or  fleshy 
parts  of  animals.  The  curd  of  milk  is  also  a  modification  of  the 
albuminous  principle.  Another  modification  of  the  same  princi- 
ple is  the  substance  called  gluten  ;  this  substance  though  most 
abundant  in  vegetables,  so  far  resembles  the  fleshy  parts  of  ani- 
mals, as  to  be,  in  like  manner,  capable  of  separation  into  two  por- 
tions, analogous  to  gelatine  and  albumen.  Neither  of  these  mo- 
difications of  albumen  exhibits  the  quality  possessed  by  gelatine, 
of  being  artificially  convertible  into  saccharine  matter  ;  at  least  by 
any  known  process  ;  but  all  of  them,  including  gelatine,  difier  from 
the  oleaginous  and  the  saccharine  principles,  in  this  respect;  tliat 
they  contain  a  fourth  elementary  principle,  namely,  azote.  The 
exact  composition  of  the  albuminous  group  cannot  at  present  be 
stated. 

Such  are  tlie  three  great  staminal  principles  from  which  all 
organized  bodies  are  essentially  constituted.  Of  these  staminal 
principles  it  has  already  been  remarked,  that,  without  changing 
ilieir  essential  composition,  they  are  capable  of  assuming  an  infi- 
nite variety  of  modified  forms  ;  many  of  which  are  so  peculiar, 
that  it  is  very  diflicult  to  recognize  their  identity,  from  their  sen- 


FOOD  OF  ANIMALS.  259 

sible  properties.  Moreover,  these  staminal  principles,  in  all  their 
forms,  are  capable  of  readily  passing  into  one  another,  and  of  com- 
bining with  each  other;  at  least  the  organic  agents,  as  \\e  shall 
see  liereafter,  have  the  power  of  effecting  these  changes.  Further, 
these  staminal  principles  are  all  susceptible  of  transmutation  into 
new  principles,  according  to  certain  laws:  llius  the  saccliarine 
principle  is  readily  convertible  into  the  acid,  termed  oxalic  ;  or, 
under  other  circumstances,  into  the  modification  of  the  oleaginous 
principle,  alcohol.  Though  an  endless  variety,  however,  of  these 
modifications  of  the  staminal  principles  exist  in  difierent  organized 
beings,  accompanied  by  numerous  foreign  bodies,  the  proportion 
they  bear  to  the  staminal  principles  is  very  limited  ;  and  they  are 
either  confined  to  glandular  secretions,  or  are  excrementitious,  or 
extravascular  :  that  is  to  say,  these  modifications  and  combinations 
form  no  part  of  the  living  animal,  though  they  are  attached  to  it ; 
as  in  the  case  of  the  various  products  of  secretion,  the  shells  of 
the  molluscous  tribes,  and  many  others. 

The  consequence  then,  to  which  we  before  alluded  is;  that  as 
all  the  more  perfect  organized  beings  feed  on  other  organized  be- 
ings, their  food  tnust  necessarily  consist  of  one  or  more  of  the 
above  three  staminal  principles.  Hence,  it  not  only  follows,  as  be- 
fore observed,  that  in  the  more  perfect  animals,  all  the  antecedent 
labour  of  preparing  these  compounds  clc  novo,  is  avoided  ;  but  that 
a  diet  to  be  complete,  must  contain  more  or  less  of  all  the  three 
staminal  principles.  Such,  at  least,  must  be  the  diet  of  the  higher 
classes  of  animals,  and  especially  of  man.  It  cannot  indeed  be 
doubted  that  many  animals  have  the  power  of  forming  a  chyle, 
and  if  expressly  organized  for  the  purpose,  may  even  live  for  a 
while  on  one  of  these  classes  of  aliments  ;  but  that  they  can  be  so 
nourished  for  an  unlimited  time, is  exceedingly  improbable.  Nay, 
if  we  judge  from  what  is  known  from  universal  observation,  as  well 
as  from  experiments  which  have  been  actually  made  by  physiolo- 
gists regarding  food,  we  are  led  to  the  directly  opposite  conclu- 
sion ;  namely,  that  the  more  perfect  animals  could  not  so  exist  ; 
but  that  a  mixture,  of  two  at  least,  if  not  of  all  the  three  classes  of 
staminal  principles,  is  necessary  to  form  an  alimentary  compound 
well-adapted  to  their  use. 

This  view  of  the  nature  of  aliments  is  singularly  illustrated  and 
maintained  by  the  familiar  instance  of  the  composition  of  Milk. 
All  other  matters  appropriated  by  animals  as  food,  exist  for  them- 
selves ;  or  for  the  use  of  the  vegetable  or  animal  of  which  they 
form  a  constituent  part.  But  milk  is  designed  and  prepared  by 
nature  expressly  as  food ;  and  it  is  the  only  material  throughout 
the  range  of  organization  that  is  so  prepared.  In  milk,  therefore, 
we  should  expect  to  find  a  model  of  what  an  elementary  substance 
ought  to  be — a  kind  of  prototype,  as  it  were,  of  nutritious  mate- 
rials in  general.  Now,  every  sort  of  milk  that  is  known,  is  a  mix- 


280  CHEMISTRY  OF  ORGANIZATION. 

ture  of  the  three  staminal  prinoiples  we  have  described  ;  that  is  to 
say,  milk  always  coiilains  a  saccharine  principle,  a  bulyraceous 
or  oil')  principle,  and  a  caseous,  or  strictly  speaking,  an  albumi- 
nous principle.  Though,  in  the  milk  of  ditlerent  animals,  these 
three  staminal  principles  exist  in  endlessly  moditied  forms,  and  in 
very  different  proportions  ;  yet  neither  of  the  three  is  ai  present 
known  to  be  entirely  wanting  in  the  milk  of  any  animal. 

Of  all  the  evidences  of  design  in  the  whole  order  of  nature, 
]\lilk  affords  one  of  t!ie  most  unequivocal.  No  one  can  for  a  mo- 
ment doubt  the  object  for  which  this  valuable  fluid  is  prepared. 
No  one  can  doubt  that  the  apparatus  by  which  milk  is  secreted 
has  been  formed  especially  for  its  secretion.  No  one  will  main- 
tain that  tlie  apparatus  for  the  secretion  of  milk  arose  from  the 
wishes  or  the  wants  of  the  animal  possessing  it,  or  from  any  fan- 
cied plastic  energy.  On  the  contrary,  the  rudiments  of  the  appa- 
ratus for  the  secretion  of  milk  must  h  ive  actually  existed  in  the 
body  of  the  animal,  ready  for  developement,  before  it  could  have 
felt  either  wants  or  desires.  In  short,  it  is  manifest  that  the  ap- 
paratus and  its  uses,  were  designed  and  made  what  they  are,  by 
the  great  Creator  of  the  universe  ;  and  on  no  other  supposition, 
can  their  existence  be  explained. 

The  composition  of  the  substances,  by  which  animals  are 
usually  nourished,  favours  the  mixture  of  the  primary  staminal 
alimentary  principles  ;  since  most  of  these  substances  are  com- 
pounds, of  at  least  two,  of  the  staminal  principles.  Thus,  most 
of  the  gramineous  and  herbaceous  matters  contain  the  saccharine 
and  the  glutinous  principles  ;  while  every  part  of  an  animal  con- 
tains at  least  albumen  and  oil.  Perhaps,  therefore,  it  is  impossi- 
ble to  name  a  substance  constituting  the  food  of  the  more  perfect 
animals,  which  is  not  essentially  a  natural  compound  of  at  least 
two,  if  not  of  all  the  three  great  principles  of  aliment.  But  it  is 
in  the  artificial  food  of  man  that  we  see  this  great  principle  of 
mixture  most  strongly  exempliiied.  He,  dissatisfied  with  the 
spontaneous  productions  of  nature,  culls  from  every  source  ;  and 
by  the  force  of  his  reason,  or  rather  of  his  instinct,  forms  in  every 
possible  manner,  and  under  every  disguise,  the  same  great  ali- 
mentary compound.  This  after  all  his  cooking  and  his  art,  how 
much  soever  he  may  be  disinclined  to  believe  it,  is  the  sole  ob- 
ject of  his  labour ;  and  the  more  nearly  his  results  approach  to 
this  object,  the  more  nearly  do  they  approach  perfection.  Even 
in  the  utmost  refinements  of  his  luxury,  and  in  his  choicest  deli- 
cacies, the  same  great  [)rinciple  is  attended  to  ;  and  his  sugar  and 
flour,  his  og(^s  and  butler,  in  all  iheir  various  forms  and  combina- 
tions, are  nothing  more  or  loss,  than  disiruised  imitations  of  the 
great  alinuMitury  prototype  milk,  as  furnished  to  him  by  nature. 


261 


CHAPTER  III. 

OF  THE  DIGESTIVE  PROCESS  ;    AND  OF  THE  GENERAL  ACTION  OF  THE 

STOMACH  AND  DUODENUM. 

We  proceed  now  to  consider  the  most  important  function  of 
the  stomach,  by  which  the  assimilation  of  the  food  is  begun. 
But  before  that  function  can  be  well  understood,  it  is  necessary  to 
make  a  (ew  remarks  on  the  influence  of  water,  in  modifying  the 
intimate  constitution  and  the  peculiar  properties  of  alimentary 
substances.  We  have  intentionally  delayed  these  remarks,  in 
order  that  in  this  place  the  chemical  influence  of  water  might  be 
more  strikingly  exemplitied. 

Water  enters  into  the  composition  of  most  organized  bodies  in 
two  separate  forms  ;  which  must  be  clearly  distinguished,  and 
which  it  is  requisite  that  the  reader  should  always  bear  in  mind. 
Water  may  constitute  an  essential  element  of  a  substance,  as  of 
sugar  or  of  starch  in  their  dryest  states  ;  in  which  case,  the  water 
cannot  be  disunited  without  destroying  the  compound  :  or  water 
may  constitute  an  accidental  ingredient  of  a  substance,  as  of  sugar 
or  of  starch  in  their  moist  states  ;  in  which  case  more  or  less  of 
the  water  may  frequently  be  removed,  without  destroying  the 
essential  properties  of  the  compound.  Now,  a  very  large  number 
of  organized  bodies,  (perhaps  all  those  to  which  our  present  in- 
quiry relates)  contain  water  in  both  these  forms  ;  both  as  an 
essential  element,  and  as  an  accidental  ingredient ;  and  in  most 
instances,  it  is  impossible  to  discriminate  between  the  water  that 
is  essential,  and  that  which  is  accidental.  The  mode  of  union, 
however,  among  the  elements  of  bodies,  in  these  two  states  of 
their  combination  with  water,  must  be  altogether  difl'erent. 
Wherein  the  difference  consists,  is  very  imperfectly  known  ;  but 
perhaps  the  following  remarks  may  throw  some  light  on  the  sub- 
ject; at  least,  they  will  serve  to  point  out,  the  nature  of  these 
two  modes  of  union,  to  the  reader. 

In  the  first  part  of  this  volume,  we  stated  that  the  molecular, 
or  combining,  weights  of  carbon  and  of  water  are,  by  chemists, 
usually  considered  to  be  represented  by  the  numbers  6  and  9  ; 
the  weight  of  hydrogen  being  one.  We  also  advanced  the  opinion, 
that  the  molecules  or  atoms  of  carbon  and  of  water,  where  more 
than  one  exist,  instead  of  remaining  separate,  as  is  now  supposed, 
are  associated  together  into  groups,  or  supermolecules  ;  and  that 
carbon,  water,  and  similar  bodies,  always  enter  into  combination, 
not  as  single  molecules,  but  as  one  supermolecule.  To  illustrate 
our  meaning,  let  us  take  as  examples,  the  state  of  combination  of 
tlie  molecules  constituting  the  different  varieties  of  sugar. 


262  CHEMISTRY  OF  ORGANIZATION. 

Sugar  from  the  cane,  in  its  purest  state,  and  when  as  free  as 
possible  from  accidental  water,  is,  according  to  the  present  lan- 
guage of  chemists,  composed  of  9  atoms  of  carbon  and  8  atoms  of 
water.  Now,  we  suppose  these  9  atoms  of  carbon,  and  8  atoms  of 
water,  to  be  associated  into  two  supermolecules,  weighing  (9x6) 
54,  and  (8x9)  72,  respectively.  So  that,  we  conceive  a  molecule 
of  sugar  from  the  cane  to  be  a  binary  compound,  of  a  supermole- 
cule  of  carbon  weighing  54,  and  a  supermolecule  of  water  weigh- 
ing 72.  Again,  the  sugar  of  honey,  according  to  the  present  lan- 
guage of  chemists,  is  composed  of  9  atonis  of  carbon,  and  12 
atoms  of  water  ;  or,  according  to  our  view  of  molecular  arrange- 
ment, the  sugar  of  honev  is  composed  of  two  supermolecules,  one 
of  them,  carbon,  weigli-iig  54,  as  in  the  sugar  of  the  cane — the 
other,  water,  weighing;-  no  less  than  (12x9)  108.  A  similar  state- 
ment may  be  given  of  tlie  composition  of  Lignin,  another  of  the 
saccharine  class  of  bodies.  This  substance,  which,  in  all  its 
various  forms  appears  to  consist  essentially  of  equal  weights  of 
carbon  and  water,  may  be  said  to  be  composed  of  9  atoms  of  j:ar- 
bon,  and  6  atoms  of  water  ;  or,  according  to  our  views,  of  two 
su  pel  molecules  weighing  (9x6)  54,  and  (6x9)  54,  respectively. 
Hence,  the  saccharine  class  of  bodies  may  be  represented  in  the 
folio winir  manner  : — 


LigTiln. 

Cane  Siig-ar  ;  Wheat  Slurch. 

Sugar  of  honey  ;   Arrowroot. 

The  molecular  constitution  of  the  saccharine  bodies,  above 
stated,  may  be  compared  with  that  of  Vinegar.  According  to  the 
present  language  of  cliemists,  vinegar,  in  its  purest  and  most  de- 
tached form,  is  composed  of  4  atoms  of  carbon,  and  3  atoms  of 
water  ;  or,  according  to  our  views,  of  two  supermolecules  weigh- 
ing (1x6)  21,  and  (3x9)  27,  respectively.  Thus,  the  molecular 
consiiiuiion  of  tliese  two  did'erent  states  of  vinegar  may  be  repre- 
sented as  follows  : — 

Carl)on.  AVater. 

24         -f-  27         Absolute  vineg-ar. 

24         -|-         36         Crystallized  or  solid  vinegar. 

We  have  stated  \hc  composition  of  vinegar,  in  order  to  draw 
the  attention  of  the  reader,  to  the  ditlerence  between  the  super- 
molecule  of  the  carbon  in  that  acid,  and  the  supermolecule  of  the 
carbon  in  the  saccharine  class  of  bodies  ;  a  diilerence  to  which 
these  two  classes  of  bodies  proliably  owe  the  striking  dillerences 
in  their  sensible  proj^erties.  J3ut  why  the  supermolecule  of  car- 
bon should  be  54  in  bodies  of  the  saccharine  class,  and  why  this 
supermolecule  shoidd  in  general  exist  in  the  sclfattraclive  form, 


Carbon. 

Water, 

54 

+ 

54 

54 

72 

54 

+ 

108 

PROCESS  OF  DIGESTION  IN  ANIMALS.  263 

and  produce  sweetness  ;  or  why  the  supeimolecule  of  carbon  in 
vinegar  should  be  24,  and  wfiy  this  supermolecule  should  have 
such  a  tendency,  as  it  exhibits,  to  assume  the  self-repulsive  form, 
and  to  produce  sourness  ;  we  do  not  know,  and  probably  shall 
never  be  able  fully  to  explain.  Still,  there  can  be  little  doubt 
that  a  careful  and  philosophical  examination  of  the  phenomena, 
would  tro  far  to  dispel  the  obscurity  in  which  the  subject  is  now 
involved. 

Such  are  the  principles,  which,  we  conceive  to  regulate  the 
chemical  union  of  organic,  and  indeed  of  all  other  compounds  ; 
and  if  chemical  union  be  so  regulated,  the  inferences  are  most 
curious  and  important.  With  these  inferences  in  general,  we 
have  at  present  no  concern  :  but  those  more  particularly  relating 
to  alimentary  compounds  are  the  following: — 

First.  We  would  draw  the  attention  of  the  reader  to  the  con- 
trast between  the  two  snpermolecules  of  carbon,  and  of  water, 
constituting  sugar  ;  the  supermolecide  of  carbon  being  uniform 
throughout  the  whole  saccharine  class,  while  the  supermolecule 
of  water  is  that  which  is  variable.  Now,  there  is  reason  to  be- 
lieve that  this  contrast  holds  in  other  instances  ;  and  that  in  dif- 
ferent organized  substances  of  the  same  kind,  the  supermolecule 
of  carbon,  or  of  some  of  its  compounds,  remains  the  permanent 
and  characteristic  element ;  and  that  the  different  modifications 
are  produced  by  variations  in  the  supermolecule  of  water ;  which 
may  be  called  the  modifying  supermolecule. 

Secondly.  The  manner  of  the  operation  of  the  modifying 
agency  may  be  thus  illustrated.  If  to  a  portion  of  cane  sugar, 
we  add  that  quantity  of  water,  which,  by  an  easy  calculation,  we 
learn  is  necessary  to  be  united  with  it,  in  order  to  its  conversion 
into  sugar  of  honey ;  we  find  that  we  cannot  succeed  in  producing 
such  conversion;  and  that  the  excess  of  water  which  had  been 
added,  flies  ofl",  and  leaves  the  cane  sugar  in  its  original  state.  On 
the  other  hand,  if  we  apply  heat  to  the  sugar  of  honey  ;  though 
we  may  indeed  drive  otl'  part  of  the  water  essentially  associated 
with  that  sugar,  we  do  not  obtain  sugar  similar  to  that  of  the  cane; 
but  we  destroy,  or  altogether  decompose  the  sugar  of  honey. 
These  facts,  therefore,  show  that  the  excess  of  water,  constituting 
the  difference  of  the  sugar  of  honey  from  the  sugar  of  the  cane, 
is  really  in  some  state  of  essential  union,  incapable  of  being  imi- 
tated ;  while,  in  the  cane  sugar,  the  water  may  exist  as  an  acci- 
dental ingredient  only.  In  fact,  according  to  our  views  of  mole- 
cular arrangement ;  every  individual  supermolecule  of  the  weaker 
sugar  contains  a  portion  of  this  excess  of  water,  as  an  essen- 
tied  element  of  its  composition.  Hence  such  water  cannot  be 
separated  from  any  compound,  without  destroying  the  entire  era- 
sis,  or  constitution,  of  its   molecular  elements  ;   which,  as  in  the 


264  CHEMISTRY  OF  ORGANIZATION. 

case  of  the  sugar  of  lioney,  we  find,  by  experiment,  to  be  the  re- 
sult. On  the  other  hand,  we  suppose  the  molecules  of  accidental 
water  to  form  no  essential  element  of  the  molecules  of  sugar,  or 
of  other  bodies,  but  to  be  only  loosely  associated  ivith  them  ;  and 
hence,  the  ease  with  which  accidental  water  may  be  separated 
without  destroying  such  bodies. 

Thirdly.  It  may  be  advanced  as  a  general  rule,  that  the  larger 
the  number,  representing  the  weight  of  the  supermolecule  of  any 
compound  substance  ;  whether  such  number  represent  the  cha- 
racteristic, or  the  modifying  supermolecule  ;  the  more  easily  may 
that  compound  substance  be  decomposed.  Thus,  the  sugar  of 
honey  is  more  easily  decomposed — is  much  less  permanent,  than 
the  sugar  of  the  cane  ;  and  the  purest  sugar,  is  much  less  perma- 
nent than  Lignin.  In  like  manner,  when  water  is  the  modifying 
element  of  any  compound,  as  it  is  in  most  organic  compounds, 
the  larger  the  number  representing  the  supermolecule  of  the  water, 
the  greater,  for  the  most  part,  is  the  solubility  of  the  compound. 

Fourthly.  There  are,  at  present,  no  chemical  terms  corre- 
sponding to  those  diflerences  of  composition,  which  we  have 
brought  under  the  notice  of  the  reader.  Now,  the  terms  strong 
and  weak,  which  in  commerce,  distinguish  the  ditTerent  varieties 
of  sugar,  are  sufficiently  expressive ;  we  have,  therefore,  made 
choice  of  them,  to  denote  the  similar  varieties  of  other  organic 
compounds.  Thus,  when  we  speak  of  a  strong  compound  ;  we 
mean  that  its  constituent  supermolccules  are,  like  those  of  strong 
cane  sugar,  less  complicated  than  the  supermolccules  of  a  weak 
principle,  like  those  of  the  sugar  of  honey.  Again,  there  are  no 
terms  expressive  of  the  conversion  of  a  strong  substance  into  a 
weak  substance,  or  the  contrary.  T.o  express  such  conversion 
we  have  adopted  the  terms  reduction,  and  completion. 

In  the  above  illustrations  of  the  modifying  influence  of  wa'er 
in  organic  compounds,  we  have  selected  sugar  as  our  example, 
solely  from  its  being  the  most  familiar.  But,  as  we  have  more 
than  once  noticed,  exactly  the  same  laws  appear  to  regulate  the 
composition  of  all  organized  bodies.  Thus  in  the  strong,  fixed, 
and  solid,  oils  or  fats,  the  ciiaracteristic  supermolecule  of  which, 
as  we  have  already  said,  has  some  relation  to  olefiant  gas  ;  the 
modifying  molecule  of  water  is  very  small,  perhaps,  in  some  olea- 
ginous bodies,  is  even  a  submolecule.  Whereas,  in  alcohol, 
which  is  the  weakest  condition  of  the  oily  principle,  the  weight 
of  the  modifying  supermolecule  of  water  is  more  than  half  that 
of  the  olctiant  gas,  and  alcohol  is  perfectly  soluble  in  water. 

(i<3laiinous  and  albuminous  substances,  also,  exhibit  precisely 
the  game  variations,  'j'lie  strong  tenacious  glue,  employed  in  tho 
arts,  is  made  from  the  firmer  parts  of  the  hides  of  old  animals  ; 
wlule  the  gelatinous  size,  or  weak  glue,  is  made  from   the  skins 


PROCESS  OF  DIGESTION  IN  ANIMALS.  265 

of  younger  and  more  delicate  animals.  These  two  varieties  of 
glue  diller  from  one  another,  in  the  weights  of  the  modifying 
supermolecules  of  water  which  enter  into  their  composition.  In 
general,  it  may  be  observed,  that  the  substances  composing  the 
frame  of  old  and  of  young  animals,  differ  chiefly  in  the  weights 
of  their  modifying  supermolecules  of  water  ;  and  that  the  dissi- 
milarity of  their  properties,  is  chiefly  owing  to  this  difference. 

If  the  reader  has  clearly  apprehended,  and  will  bear  in  mind, 
the  principles  that  have  now  been  stated,  as  regulating  the  che- 
mical constitution  of  organized  bodies,  and  the  modes  in  which 
they  are  influenced  by  their  modifying  constituent,  water ;  he 
will  be  able  to  accompany  us  in  the  observations  we  are  about  to 
offer  ;  and  he  will  thus,  more  especially,  be  able  to  form  a  gene- 
ral conception  of  the  chemical  operations  of  the  stomach.  The 
operations  of  the  stomach,  viewed  as  a  whole,  may  be  stated  as 
follows  : — 

1.  The  stomach  has  the  power  of  dissolving  alimentary  sub- 
stances, or,  at  least  of  bringing  them  to  a  semifluid  state.  This 
operation  seems  to  be  altogether  chemical ;  and  is  probably  ef- 
fected by  reducing  the  properties  of  these  alimentary  substances. 

2.  The  stomach  has,  within  certain  limits,  the  power  of  chang- 
ing into  one  another,  the  simple  alimentary  principles,  which 
have  been  described  in  the  last  chapter.  Unless  the  stomach 
possessed  such  a  power,  that  uniformity  in  the  composition  of 
the  chyle,  which  we  may  imagine  to  be  indispensable  to  the  ex- 
istence of  every  animal,  could  not  be  preserved.  This  part  of  the 
operations  of  the  stomach,  appears,  like  the  reducing  process,  to 
be  chemical ;  but  not  so  easy  of  accomplishment ;  it  may  be 
termed  the  converting  operation  of  the  stomach. 

3.  The  stomach  must  have,  within  certain  limits,  the  power  of 
organizing  and  vitalizing  the  different  alimentary  substances ; 
so  as  to  render  them  fit  for  being  brought  into  more  intimate  union 
with  a  living  body,  than  the  crude  aliments  can  be  supposed  to 
be.  It  is  impossible  to  imagine,  that  this  organizing  agency  of 
the  stomach  can  be  chemical.  This  agency  is  vital,  and  its  nature 
is  completely  unknown. 

1.  Of  the  Reducing  Powers  of  the  Stomach. — In  order  to 
render  more  intelligible  that  function  of  the  stomach,  which  it 
owes  to  its  reducing  power,  let  us  endeavour  to  trace  the  series 
of  phenomena,  which  appear  to  arise  during  the  conversion  of 
simple  albuminous  matter  into  the  albumen  of  the  chyme  ;  with- 
out taking  into  account  any  other  change. 

When  a  portion  of  fluid  albumen,  as  of  the  white  of  an  egg,  or 
of  milk,  is  introduced  into  the  stomach  of  an  animal,  as  of  a  dog, 
it  instantly  becomes  solid  ;  or,  in  ordinary  language,  is  coagulated. 
This  coagulation  is  probably  a  mere  chemical  change ;  for  the 

23 


266  CHEMISTRY  OF  ORGANIZATION. 

same  change,  would,  under  similar  circumstances,  take  place  out 
of  liie  body.     That  is  to  say,  if  the  white  of  an  egg,  or  milk, 
were  mixed  with  a  fluid  more  or  less  acid,  like  that  which  exists 
in  the  stomachs  of  animals  while  the  food  is  undergoing  the  pro- 
cess of  digestion  ;  it  would  be  coagulated.     There  may  be,  how- 
ever, and  i)robably  is,  some  object  in  the  change  produced  by 
coagulation  ;  since  the  stomachs  of  animals  are  fitted  to  operate 
chiefiy  on  solid  matters.     Admitting  the  object  of  the  change,  we 
can  hardly  consider  it  to  be  essential  to  the  subsequent  process ; 
for  gelatine,  a  staminal  alimentary  principle,  nearly  resembling 
albumen  in  its  composition,  undergoes,  under   similar   circum- 
stances, no  such  solidifying  cliange.     The  albumen  thus  solidified 
by  the  stomach  into  a  mass  or  curd,  is  soon  altered  further ;  more 
especially  that  part  of  the  mass,  with  which  the  membrane  of  the 
stomach  is  in  contact.     The  curdy  mass  assumes  a  gelatinous 
appearance  ;  then  each  portion  is  successively  more  and  more 
softened,  till  at  length,  the  whole  becomes  nearly  fluid,  and  after 
some  additional  modifications,  gradually  passes  into  the  state  of 
chyme.     Through  all  these  apparent  changes,  however,  the  al- 
bumen has  undergone  no  real  change.  What  was  introduced  into 
the  stomacli  as  albumen,  is  still  albumen  in  the  chyme  ;  at  least 
chemists  have  pronounced  it  so  to  be.     Yet  it  has  assumed  an 
appearance  altogether  different.     The  albumen  of  the  egg^  out  of 
the  stomach,  may  be  coagulated  by  heat,  into  a  firm  elastic  solid. 
The  albumen  of  the  chyme  is  indeed  coagulable  by  heat,  but  its  co- 
agulation is  so  imperfect,  and  so  wanting  in  tenacity,  as  to  offer  a 
striking  contrast  with  the  coagulated  albumen  of  the  egg.  What  then, 
in  the  stomach,  has  liappened  to  the  albumen  ?  Viewing  only  its 
susceptibility   of  coagulation,  the    albumen  has  merely   become 
chemically  combined  with  a  portion  of  water.     The  solid  and  te- 
nacious albumen  has,  by  this  combination  with  water,  been  re- 
duced to  the  weakest  possible  state — to  the  delicate  state,  as  it 
were,  of  infancy  ;  in  short,  to  a  state  precisely  analogous  to  that 
of  the  weak  sugars,  and  other  organic  compounds,  as   compared 
with  the  strong  and  perfect  varieties  of  the  same  substances,  de- 
scribed in  the  preceding  chapter. 

Such  is,  we  believe,  an  accurate  account  of  the  merely  solvent 
or  reducing  powers  of  the  stomach.  We  have  next  to  show  the 
means  by  which  this  solution  or  reduction  is  efTected. 

The  process  of  combining  diflerent  substances  MMth  water,  and 
of  thus  reducing  them  from  a  stronger  to  a  weaker  condition, 
may,  in  some  instances,  and  to  a  certain  degree,  be  effected  arti- 
ficially, lint  in  no  instance  do  we  appear  to  be  able  to  invert 
tlie  process  ;  or  to  complete  an  organic  compound,  by  again 
separating  the  water.  For  example,  we  can,  in  some  respects, 
make  a  strong  sugar  weak,  but  we  cannot  change  a  weak  into  a 


PROCESS  OF  DIGESTION  IN  ANIMALS.  267 

Strong  sugar;  though  such  a  change,  within  certain  limits,  seems 
to  be,  to  the  organic  agents,  just  as  easy,  as  the  reducing  process. 

The  difTerent  operations  of  cookery,  as  roasting,  boiling, 
baking,  &c.  have  all  a  reducing  efTect ;  and  may,  tlierefore,  be 
considered  as  preparatory  to  the  solvent  action  of  the  stomach. 
Of  these  operations,  Man's  nature  has  taught  him  to  avail  him- 
self, and  they  constitute  the  chief  means  by  which  he  is  enabled 
to  be  omnivorous  :  for,  without  such  a  preparation,  a  very  large 
portion  of  the  matters  which  he  now  adopts  as  food,  would  be 
completely  indigestible.  By  different  culinary  processes,  the 
most  refractory  substances,  can  often  be  rendered  nutritious. 
Thus,  by  alternate  baking  and  boiling,  the  woody  fibre  itself  may 
be  converted  into  a  sort  of  amylaceous  pulp  ;  not  only  possessing 
most  of  the  properties  of  the  amylaceous  principle,  but  capable 
of  being  formed  into  bread.  Tlie  culinary  art  eng-a^es  no  small 
share  of  attention  among  m.ankind;  but,  unfortunately,  cooks  are 
seldom  chemists  ;  nor  indeed  do  they  understand  the  most  simple 
of  the  chemical  principles  of  their  art.  Hence,  their  labour  is 
most  frequently  employed,  not  in  rendering  wholesome  articles 
of  food  more  digestible,  which  is  the  true  object  of  cookery  ;  but 
in  making  unwholesome  things  palatable :  foolishly  imagining 
that  what  is  agreeable  to  the  palate,  must  be  also  healthful  to  the 
stomach.  A  greater  fallacy  can  scarcely  be  conceived ;  for, 
though  by  a  beautiful  arrangement  of  Providence,  what  is  whole- 
some is  seldom  disagreeable  ;  the  converse  is  by  no  means  appli- 
cable to  man  ;  since  those  things  which  are  pleasant  to  the  taste 
are  not  unfrequently  very  injurious.  Animals,  indeed,  for  the 
most  part,  avoid,  instinctively,  all  unwholesome  food  ;  probably 
because  everytiiing  tiiat  would  be  prejudicial,  is  actually  distaste- 
ful to  them.  But  as  regards  man,  the  choice  of  articles  of  nou- 
rishment has  been  left  entirely  to  his  reason. 

In  order  to  illustrate  the  importance  of  a  judicious  adaptation  of 
cookery,  we  may  observe,  that  the  particular  function  of  the 
stomach,  now  under  consideration,  namely,  the  dissolving  or  re-' 
ducing  function,  is  liable  to  very  great  derangements.  In  some 
individuals,  the  reducing  pov/er  is  so  v/eak,  that  their  stomach  is 
almost  incapable  of  dissolving  solid  food  of  the  most  simple  kind. 
In  such  a  state  of  the  stomach,  a  crude  diet  of  the  flesh  of  animals 
in  a  hardened  state,  or  of  other  compact  substances,  is  litde  else 
than  poisonous  ;  while  the  same  animal  and  vegetable  matters 
often  agree  well,  if  reduced  to  a  pulpy  slate.  On  the  other  hand, 
as  in  the  disease  termed  Diabetes,  the  solvent  powers  of  the  sto- 
mach are  often  inordinately  increased  ;  and  every  article  of  food 
is  dissolved  and  absorbed  almost  as  soon  as  it  is  swallowed.  In 
such  cases,  a  diet  and  a  mode  of  preparation  are  required,  directly 
the  reverse  of  those  which  are  found  to  be  so  beneficial,  when 


268  CHEMISTRY  OF  ORGANIZATION. 

there  is  a  debility  of  the  solvent  powers  ;  and  aliments  which  are 
firm  and  solid,  but  at  the  same  time  nutritious,  must  be  chosen. 

Regarding  the  intimate  nature  of  the  agency,  by  which  the 
combination  of  alimentary  substances  with  water  is  effected  in 
the  stomach,  we  cannot  be  said  to  possess  much  certain  know- 
ledge. This  combination  appears  to  be  chiefly  owing  to  the 
agency  of  a  fluid,  secreted  by  the  stomach  ;  the  glands  for  the 
formation  of  which  fluid,  are  most  numerous  toward  the  pyloric 
orifice.  The  aliment  having  been  previously  broken  down  by 
mastication,  and  havinjj  received  an  admixture  of  saliva  and  of 
other  fluids,  is  brought  into  contact  with  the  fluid  secreted  by  the 
stom.ach ;  by  which  secretion,  or  by  some  other  energy  there  in 
operation,  the  food  that  has  been  introduced  into  the  stomach  is 
associated  with  water ;  and  thus  becomes  itself  more  or  less  a 
fluid.  Of  this  important  secretion  of  the  stomach,  chlorine ,  in 
some  state  or  other  of  combination,  is  an  ingredient ;  it  would 
seem  a  necessary  ingredient ;  for  the  secretion  in  its  healthy 
slate,  always  contains  more  or  less  of  chlorine,  the  powerful  in- 
fluence of  which  elementary  principle,  seems  mainly  to  contribute 
towards  efTccting  the  union  of  the  food  with  water.  The  chlo- 
rine, thus  so  indispensable  to  the  reducing  process,  is  perhaps 
more  frequently  the  subject  of  derangement,  than  anything  con- 
cerned with  the  assimilation  of  the  food.  It  often  happens  that 
instead  of  chlorine,  or  a  little  free  muriatic  acid,  a  large  quantity 
of  free  muriatic  acid  is  elicited  ;  which  not  only  gives  rise  to  much 
secondary  uneasiness,  but  more  or  less  retards  the  process  of  re- 
duction itself.  The  source  of  this  chlorine  or  muriatic  acid,  must 
be  the  common  salt  which  exists  in  the  blood  :  to  suppose  that  it 
is  generated,  is  quite  an  unnecessary  hypothesis.  Tiie  chlorine 
is  therefore  secreted  from  the  blood  ;  and  it  may  be  demanded, 
what  is  the  nature  of  the  agency,  capable  of  separating  that  ele- 
ment from  a  fluid  so  heterogeneous  as  the  blood?  We  are  ac- 
quainted with  one  agent  that  exerts  such  a  power,  namely,  elec- 
tricity ;  and  this  agent,  as  we  formerly  observed,  seems  to  be 
employed  by  the  animal  economy  for  its  operations,  in  the  same 
manner,  and  on  the  same  principles,  as  the  materials  themselves 
are  employed,  from  whicli  the  animal  body  is  constructed.  Per- 
haps, therefore  the  decomposition  of  the  salt  of  the  blood  may  be 
fairly  referred  to  the  immediate  agency  of  this  princi])le,  elec- 
tricity. But  here  the  question  arises,  What  becomes  of  the  soda 
from  which  the  muriatic  acid  has  been  disunited  ?  The  soda  re- 
mams  behind,  of  course,  in  the  blood,  and  a  portion  of  it  no  doubt, 
is  requisne  to  preserve  the  weak  alkaline  condition  essential  to 
the  fluidity  of  the  blood,  liut  the  larger  part  of  this  soda  is  pro- 
bably directed  to  the  liver,  and  is  elicited  with  the  bile  in  the 
duodenum,  where  it  is  thus  again  brought  into  union  with  the 
acid,  tiiat  had  been  separated  from  the  blood,  by  the  stomach. 


PROCESS  OF  DIGESTION  IN  ANIMALS.  269 

These  observations,  illustrating  the  importance  of  common  salt  in 
the  animal  economy,  seem  to  explain,  in  a  satisfactory  manner, 
that  instinctive  craving  after  this  substance,  which  is  shown  by 
all  animals. 

Admitting  that  the  decomposition  of  the  salt  of  the  blood  is 
owing  to  the  immediate  agency  of  galvanism  ;  we  have,  in  the 
principal  digestive  organs,  a  kind  of  galvanic  apparatus,  of  which 
the  mucous  membrane  of  the  stomach,  and  perhaps  that  of 
the  intestinal  canal  generally,  may  be  considered  as  the  acid  or 
positive  pole ;  while  the  hepatic  system  may,  in  the  same 
view,  beconsidered  as  the  alkaline  or  negative  pole.  Whether 
such  galvanic  action  be  admitted  or  not ;  and  the  admission  is 
of  no  very  great  importance  ;  what  we  have  above  stated  may  be 
received  as  a  simple  expression  of  the  facts,  in  so  far  as  they 
relate  to  the  saline  constituents  of  the  blood.  Moreover,  be  the 
nature  of  the  energies  what  they  may,  by  which  these  changes 
are  effected;  along  with  these  changes,  and  probably  by  the  aid 
of  the  same  energies,  other  very  important  changes  or  processes 
are  carried  on,  to  some  of  which  we  shall  presently  have  occa- 
sion to  allude.  In  the  mean  time,  we  may  close  this  section  by 
observing  that  there  is  strong  reason  to  believe,  that  the  solvent 
power,  which  we  have  described,  or  some  power  having  a  great 
resemblance  to  it,  exists  not  only  in  the  stomach,  but  m  every 
part  of  an  animal  body.  In  all  animals  there  are  minute  tubes, 
called  absorbents,  which  originate  in  every  part  of  their  bodies,  and 
at  length  uniting,  enter  the  sanguiferous  system  along  with  the 
chyle.  Now,  the  office  of  these  tubes,  is  to  remove  all  those 
portions  of  the  animal  frame,  which  after  having  performed  their 
several  functions,  require  to  be  withdrawn.  Of  course,  before 
solid  parts  can  be  thus  removed,  they  must  be  dissolved,  {digested 
in  fact ;)  and  such  solution,  in  many  instances,  is  probably  eliected, 
as  it  is  in  digestion,  by  combining  these  solid  parts  with  water. 
This  supposed  analogy  between  the  solvent  powers  of  the  sto- 
mach, and  those  which  must  prevail  all  over  the  body,  seems  to 
be  strongly  confirmed  by  that  similarity  of  structure  and  of  func- 
tion existing  between  the  lacteals  and  the  absorbents  :  they  in- 
deed form  but  one  system.  We  shall  resume  this  subject  here-- 
after. 

2.  Of  the  Poivers  of  Conversion  possessed  by  the  Stomach. — ^ 
Though  the  proportions  of  the  ditTerent  ingredients  of  the  chyle, 
as  ultimately  formed,  are  liable  to  be  much  varied,  according  to 
the  nature  of  the  food  ;  yet,  whatever  the  nature  of  the  food  may 
be,  the  general  composition  and  character  of  the  chyle,  remain  al- 
ways the  same.  The  stomach  must,  therefore,  be  endowed  with 
a  power  or  faculty,  the  agency  of  which  is  to  secure  this  uniform 
composition  of  the  chyle,  by  appropriate  action  upon  such  mate- 

23* 


270  CHEMISTRY  OF  ORGANIZATION. 

rials,  as  circumstances  may  bring  within  its  reach.  Two,  indeed, 
of  the  chief  materials  from  which  chyle  is  formed,  namely,  the 
albuminous  and  the  oleaginous  principles,  may  be  considered  to 
be  already  fitted  for  the  purposes  of  the  animal  economy,  without 
undergoing  any  essential  change  in  their  composition.     But  the 
saccharine  class  of  aliments,  which  form  a  very  large  part  of  the 
food  of  all  animals,  except  of  those  subsisting  entirely  on  flesh, 
are  by  no  means  adapted   for  such  speedy  assimilation.     Indeed, 
one  or  more  essential  changes  must  take  place  in  saccharine  ele- 
ments, previously  to  their  conversion,  either  into  the  albuminous, 
or  into  the  oleaginous  principles.    Most  probably,  under  ordinary 
circumstances,  these  essential  clianges  are  altogether  chemical; 
that  is  to  say,  they  are  such  as  do  take  place,  or  rather,  such  as 
would  take  place,  if  the  elements  of  the  substances  thus  changed 
in  the  stomach,  could,  out  of  the  body,  be  so  collocated,  as  to  bring 
into  action  the  affinities  necessary  to  produce  these  changes.   Thus, 
as  we  know,  the  saccharine  principle  spontaneously  becomes  al- 
cohol; M'hich,  as  has  been  stated,  is  merely  an  oleaginous  body 
of  a  weak  kind.     When,  therefore,  in  the  stomach,  it  is  requisite 
that  sugar  be  converted  into  oil,  it  is  probable  that  the  sugar  passes 
through  precisely  the  same  series  of  changes  it  undergoes,  out  of 
the  body,  during  its  conversion  into  alcohol.     We   cannot  trace 
the  conversion  of  sugar  into  albumen  ;  because  we  are  ignorant 
of  the  relative  composition,  and  of  the  laws  which  regulate  the 
changes,  of  these  two  substances.    The  origin  of  the  azote  in  the 
albumen,  is  likewise  at  present  unknown  to  us  ;  though  \n  all  or- 
dinary cases,  it  seems  to  be  appropriated  from  some  external  source. 
That  the  oleaginous  principle  may  be  converted  into  most,  if  not 
into  all  the  matters  necessary  for  the  existence  of  animal  bodies, 
seems  to  be  proved  by  the  well-known  fact,  that  the  life  of  an  ani- 
mal may  be  prolonged  by  the  absorption  of  the  oleaginous  matter, 
contained  within  its  own  body.  Thus,  many  hybernating  animals, 
when  they  retire  in  autumn,  to  sleep  during  the  winter,  are  enor- 
mously I'ai.  But  while  tlicy  sleep,  their  fat  is  gradually  removed  ; 
till  they  awake  in  the  spring  quite  divested  of  it,  and  in  a  state  of 
inanition. 

Tlie  reader  will  have  remarked  that  we  have  made  use  of  the 
term  onlinury  circumstances  ;  and  perhaps  it  may  not  be  amiss 
to  explain  what  meaning  we  attach  to  that  term. 

Wlien  an  animal  is  duly  fed  according  to  that  diet  which  is  na- 
tural to  it,  and  for  which  its  organization  has  been  adapted  ;  a  re- 
gular and  urdimirij  series  of  changes  takes  place  within  the  animal, 
and  the  alimentary  matters  are  converted  into  chyle.  But  one 
general  characteristic  of  organized  beings  is  that  within  certain 
limits,  and  for  a  certain  lime,  they  possess  the  power  of  varying 
their  habits,  and  of  accommodating  themselves  to  circumstances. 
Under    cxtraordinanj   circumstances,    therefore,    extraordinary 


PROCESS  OF  DIGESTION  IN  ANIMALS.  271 

changes  must,  and  do,  take  place.  In  some  instances,  these  changes 
out  of  the  ordinary  course,  are  to  an  extent  altogether  astonish- 
ing ;  and  such  as  defy  our  utmost  calculation.  The  assimilating 
organs  appear  even  to  decompose  principles  which  are  still  con- 
sidered as  elementary,  nay,  to  form  azote  or  carbon ;  so  that  it  is 
impossible  to  define  what,  on  an  emergency,  these  organs  are  ca- 
pable of  doing.  But  what  is  thus  done  by  these  organs  on  an 
emergency,  will  usually,  be  found  to  constitute  an  exception  to 
what  they  do  in  ordinary  ;  their  ordinary  mode  of  action  being  al- 
ways that  which  is  most  simple,  and  which  is  thus  to  be  consi- 
dered as  the  rule. 

3.  Of  the  Organizing  and  Vitalizing  Powers  of  the  Sto- 
mach.— In  this  part  of  our  investigation,  we  meet  the  real  diffi- 
culties we  have  to  overcome  in  explaining  the  operations  of  living 
beings.  The  whole  of  the  great  and  essential  changes  which  ali- 
mentary substances  undergo,  may,  and  perhaps  will  be,  traced  by 
care  and  attention  ;  but  all  beyond,  will  probably  remain  for  ever 
unknown  to  us.  Now  at  least,  it  may  be  truly  said,  that  though 
we  understand,  in  some  degree,  the  chemical  changes  ;  of  the  vi- 
talizing influence  Ave  know  absolutely  nothing.  There  is,  how- 
ever, every  reason  to  believe  that  vitality  is  imparted  through  the 
agency  of  the  living  animal  itself.  For  though,  from  the  natural 
composition  of  alimentary  substances,  they  be  to  a  certain  extent, 
fitted  for  the  purposes  of  the  animal  economy  ;  yet,  alone,  they 
are  incapable  of  uniting  themselves  with  the  animal  frame  ;  and 
unless  the  living  economy  contribute  likewise  its  share  of  the  la- 
bour, the  future  work  of  assimilation  wdll  be  incomplete. 

Of  the  Changes  the  lood  undergoes  in  the  Duodenum. — We 
alluded  in  general  terms  to  the  bile  and  the  pancreatic  fluids,  when 
we  were  treating  of  the  organs  by  which  they  are  secreted.  We 
have  now  to  consider,  more  particularly,  the  nature  of  these  se- 
cretions, and  their  share  in  the  performance  of  the  functions  of  the 
duodenum. 

With  the  yellow  colour,  and  the  intensely  bitter  taste  of  the 
hile,  all  are  familiar:  we  need  not,  therefore,  dwell  on  the  sensible 
properties  of  the  secretion,  but  proceed  to  notice  its  chemical  com- 
position. The  chemical  composition  of  the  bile  is  very  heteroge- 
neous, though  not  perhaps  so  heterogeneous  as  has  been  repre- 
sented ;  since  it  is  probable  that  many  of  the  ingredients  said  to  be 
contained  in  the  secretion,  are  products  that  have  resulted  from  the 
methods  employed  in  its  analysis.  Bile,  like  all  animal  fluids,  is 
composed  essentially  of  water  ;  but  the  solid  matters  contained  in 
the  bile,  are  nearly  altogether  formed  from  one  or  more  proximate 
principles,  in  which  carbon  and  hydrogen  predominate.  These 
proximate  principles  exist  simultaneously,  if  not  in  conjunction 
with  soda,  and  with  various  salts  of  soda,  besides  other  substances. 
The  properties  of  the  bile  vary  somewhat  in  different  animals  ; 


272  CHEMISTRY     OF  ORGANIZATION. 

but  in  all  animals  its  essential  characters  remain  wonderfully  si- 
milar. 

We  are  much  less  acquainted  with  the  properties  of  the  pan- 
creatic J^uid,  than  with  those  of  the  bile.  The  nature  of  the  pan- 
creatic fluid  was  formerly  supposed  to  be  very  analogous  to  that 
of  the  saliva;  but  recent  observations  have  shown  that  it  contains 
albumen,  and  a  curdy  substance.  The  pancreatic  fluid  is,  for  the 
most  part,  in  a  slight  degree  acid,  and  holds  in  solution  matters 
of  a  saline  nature,  closely  resembling  those  found  in  all  animal 
fluids. 

When  the  food  that  has  undergone  the  first  process  of  digestion 
in  the  stomach,  quits  that  organ,  and  enters  the  duodenum,  some 
other  clianges  of  a  very  remarkable  kind  take  place.  If  the  food 
originally  contained  no  albuminous  matter,  no  albumen  is  deve- 
loped in  the  stomach;  but  immediately  on  the  entrance  of  the 
semi-fluid  mass  into  the  duodenum,  and  its  mixture  with  the  bile 
and  the  pancreatic  fluids  ;  albuminous,  and  other  chylous  matters, 
become  distinctly  perceptible.  At  the  same  instant,  those  fluid 
parts,  which  in  the  stomach  were  acid,  are  so  far  altered,  by  the 
addition  of  the  bile,  and  the  pancreatic  fluids,  as  to  become  neu- 
tral, or  almost  neutral :  some  gas  is  frequently  extricated  ;  and 
that  portion  of  the  food  which  is  destined  to  be  excrementitious, 
is  evidently  separated.  The  albumen,  which  is  tlius  found  to 
exist  in  the  chyme,  (as  the  food  is  termed,  after  it  has  been  acted 
on  by  the  stomach,  and  has  entered  the  duodenum),  may  be  partly 
derived  from  the  pancreatic  fluid,  which,  as  we  have  already 
mentioned,  has  been  said  to  contain  albumen.  But  the  quantity 
of  albumen,  and  of  other  proximate  principles  of  the  chyle,  that 
are  found  in  the  contents  of  the  duodenum,  at  some  distance  on- 
ward from  the  pylorus,  is  much  too  great  to  be  explained  in 
this  manner.  Indeed,  the  properties,  as  well  as  the  quantity,  of 
the  albuminous  matters,  show,  beyond  a  doubt,  tliat  the  albumi- 
nous matters  are  developed  from  the  food,  and  constitute  the  chyle, 
which  is  subsequently  taken  up  by  the  lacteals. 

Such  are  those  most  interesting,  and  at  the  same  time  obvious, 
phenomena,  that  are  observed  in  different  animals,  in  which  the 
changes  produced  on  the  food  by  the  action  of  the  duodenum  have 
been  examined.  These  phenomena  appear  to  vary  considerably, 
according  to  the  nature  of  the  food  ;  but  so  far  as  we  can  under- 
stand the  phenomena,  under  every  change  of  food,  the  essential 
chiiracter  of  the  chanjies  which  the  food  underscoes  in  the  duode- 
nuiii,  remains  unaltered.  That  is  to  say  :  the  acid  formed  in  the 
stomach,  combines,  in  the  duodenum,  with  the  alkali  of  the  bile; 
the  albuminous  principles  are  developed;  and  the  excrementitious 
matters  arc,  more  or  less  perfectly,  separated.  Of  the  nature  of 
the  more  recondite  and  vitalizing  changes  which  take  place  in  the 


PROCESS  OF   DIGESTION  IN  ANIMALS.  273 

duodenum  ;  we  are  in  the  same  slate  of  complete  ignorance,  as 
we  are  of  the  similar  changes  which  lake  place  in  the  stomach, 
and  probably  shall  long  so  remain. 

In  the  preceding  remarks  on  the  different  processes  which  take 
place  in  the  stomach  and  duodenum,  and  which  are  necessary  for 
the  conversion  of  the  food  of  an  animal  into  the  living  material 
of  its  body  ;  we  have  endeavoured  to  distinguish  between  what,  to 
a  certain  extent,  is  within  our  powers  of  comprehension,  and 
what  is  completely  beyond  them.  It  remains  to  be  observed  in 
conclusion,  that  though  the  three  great  and  essential  processes  of 
digestion,  namely,  the  reducing,  the  converting,  and  the  organi- 
zing processes  be  sufficiently  distinct  from  each  other  ;  yet  it  is 
not  to  be  understood  that  they  take  place  in  succession,  or  in  the 
order  in  which  they  have  been  described.  The  fact  is,  that  all 
these  processes  go  on  at  the  same  time ;  and  as  soon  as  a  portion 
of  food  begins  to  be  dissolved,  its  future  changes  seem  to  be  de- 
termined. If  it  be  necessary  that  the  portion  of  food  undergo  an 
essential  change,  that  change  is  accordingly  begun.  If  no  such 
change  be  required,  the  organizing  process  itself  begins  simulta- 
neously with  the  reducing  process.  The  consequence  of  this 
union  of  the  digestive  processes  is,  as  we  have  stated,  that  the 
staminal  principles  are  all  developed  in  the  chyle  ;  as  soon  as  the 
excreraentitious  matters  are  separated  by  the  biliary  and  pancrea- 
tic fluids. 

Of  the  Fiindions  of  the  JUimentary  Canal,  beyond  the  Duo- 
denum.— Compared  with  the  functions  of  the  stomach  and  duo- 
denum, the  functions  of  the  succeeding  portions  of  the  alimentary 
canal,  as  far  as  we  can  judge,  are  unimportant.  The  digested 
mass  passes  from  the  duodenum  into  the  jejimum,  and  ilium  ; 
though  before  the  food  reaches  the  end  of  the  ilium,  the  whole  of 
the  chyle  contained  in  it,  has  been  absorbed  into  the  apertures  of 
the  numerous  tubes  named  lacteals.  These  tubes  open  in  greater 
or  less  number,  into  the  whole  interior  surface  of  the  three  por- 
tions of  the  alimentary  canal,  along  which  the  food  is  moved  from 
the  stomach  to  the  colon.  From  the  ilium,  the  undigested  or 
excremenlitious  matters  proceed  into  the  coecura  ;  in  which  cavity, 
in  some  animals,  as  for  example,  in  the  horse,  even  these  excre- 
menlitious matters  appear  to  undergo  a  second  digestion  ;  but  in 
all  animals,  the  contents  of  the  coecum  have  a  very  different  as- 
pect from  those  of  any  part  of  the  alimentary  canal,  nearer  to  the 
stomach.  The  mass  of  excremenlitious  matters  continue  their 
course  from  the  coecum  into  the  colon,  where  thev  are  still  further 
changed.  The  nature  of  these  changes,  however,  is  not  well 
understood,  thougii  they  are  probably  of  no  small  importance  in 
the  animal  economy.     Finally,  all  the  nutritious  portions  of  the 


274  CHEMISTRY  OF  ORGANIZATION. 

food,  liaving  entered  into  the  system  of  the   animal,   nothing  re- 
maitis  but  what  is  entirely  excrcmenlitious. 

Such  is  a  short  sketch  of  the  phenomena  of  digestion  and  assi- 
milation, in  as  far  as  these  processes  are  effected  by  the  stomach 
and  th.e  alimentary  canal.  The  phenomena  suggest  the  following 
reflections  : 

First.  With  regard  to  the  nature  and  the  choice  of  aliments, 
and  the  modes  of  their  culinary  preparation;  it  follows  from  the 
observations  we  have  offered  ;  that,  under  similar  circumstances, 
those  articles  of  food,  which  are  the  least  organized,  must  be  the 
most  difficult  to  be  assimilated  :  consequently,  that  the  assimila- 
tion of  crystallized,  or  very  pure  substances,  must  be  more  diffi- 
cult, than  the  assimilation  of  any  others.  Thus,  pure  sugar,  pure 
alcohol,  and  pure  oil,  are  much  less  easy  to  be  assimilated,  than 
substances  purely  amylaceous  ;  or  than  that  peculiar  condition  or 
mixture  of  alcohol  existing  in  natural  wines;  or  than  butter.  In 
these  forms,  the  assimilation  of  the  saccharine  and  the  oleaginous 
principles  is  comparatively  easy.  Of  all  crystallized  matters, 
pure  sugar  is  perhaps  the  most  easily  assimilated  ;  but  every  one 
is  taught  by  experience,  that  much  less  can  be  eaten  of  articles 
composed  of  sugar,  than  of  those  composed  of  amylaceous  mat- 
ters. In  some  forms  of  dyspepsia,  the  effect  of  pure  sugar  is 
most  pernicious;  perhaps  fully  as  pernicious  as  that  of  pure  al- 
cohol. Nature  has  not  furnished  either  pure  sugar  or  pure  starch ; 
and  these  substances  are  always  the  results  of  artificial  processes, 
more  or  less  elaborate  ;  in  which,  as  in  many  of  the  processes  of 
cookery,  man  has  been  over-officious  ;  and  has  studied  the  grati- 
fication of  his  palate,  rather  than  followed  the  dictates  of  his  reason. 
In  many  dyspeptic  individuals,  the  assimilating  and  preservative 
powers  of  the  system,  are  already  so  much  weakened,  as  to  be 
unable  to  resist  the  crystallization  of  a  portion  of  their  fluids. 
Thus  in  gouty  invalids,  how  often  do  we  see  chalk-stones  formed 
in  every  joint?  Now,  with  so  little  control  over  their  own  fluids, 
how  can  they  reasonably  hope  to  assimilate  extraneous  crystal- 
lizations? If,  therefore,  such  an  invalid,  on  sitting  down  to 
a  luxurious  modern  banquet,  composed  of  sugar,  and  oil,  and 
albumen,  in  every  state  of  combination,  except  those  best  adapted 
for  food,  would  pause  a  moment,  and  ask  himself  the  question ; 
Is  this  debilitated  and  troublesome  stomacii  of  mine,  endowed 
with  the  alchemy  requisite  for  the  conversion  of  all  these  things 
into  wholesome  flesh  and  blood  ?  He  would  probably  adopt  a 
simpler  repast,  and  would  thus  save  himself  from  much  uneasi- 
ness. The  truth  is,  that  many  of  the  elaborate  dishes  of  our  in- 
genious continental  neighbours,  are  scarcely  nutritious,  or  designed 
to  be  so.  Th(?y  are  mere  vehicles  for  dilferent  stimuli — diflerent 
ways,  in  short,  of  gratifying  that  low  animal  propensity,  by  which 


PROCESS  OF  DIGESTION  IN  ANIMALS.  275 

SO  many  are  urged  to  the  use  of  ardent  spirits,  or  of  various  nar- 
cotics. In  one  respect  indeed,  namely,  tiiat  of  reducing  to  a  state 
of  pulp  those  refractory  substances  which  we  have  before  men- 
tioned, the  culinary  processes  of  our  neighbours  are  much  supe- 
rior to  ours  ;  but  in  nearly  every  other  respect,  and  most  of  all, 
in  tlie  general  use  of  pure  sugar  and  pure  oil,  their  cookery  is 
eminently  injurious  to  all  persons  who  have  weak  digestion.  On 
the  other  hand,  in  this  country,  we  do  not  in  general  pay  suffi- 
cient attention  to  the  reducing  processes  of  the  culinary  art.  Every- 
thing is  firm  and  crude  ;  and  though  the  mode  of  preparation  be 
less  captivating ;  the  quantity  of  indigestible  aliment  is  quite  as 
great  in  our  culinary  productions,  as  in  those  of  France. 

We  are  not,  however,  writing  a  treatise  on  cookery  or  dietetics  ; 
but  in  treating  of  the  function  of  digestion,  it  is  im{)ossib!e  alto- 
gether to  pass  over  these  important  subjects.     The  foregoing  ob- 
servations are  merely  intended  as  illustrations  of  those  general 
principles  which  often  regulate  the  choice,  and  the  preparation  of 
the  food  of  mankind,  in  a  state  of  civilized  society.     Reason  is 
too  little  followed,  the  indulgence  of  the  palate  is  the  sole  object ; 
so  that  the  organs  of  digestion  already  enfeebled,  and  incapacitated 
for  the  assimilation,  even  of  the  most  proper  nourishment,  are 
daily  oppressed  with  a  task  for  which  they  are  altogether  unequal. 
The  consequence  is,  that  though  for  a  time  the  labourbe  sustained, 
the  digestive  energies  are  at  length  overcome.     The  dyspeptic 
being  passes  half  his  days  in  misery ;  his  offspring  inherit  their 
parents'  constitution ;  and  if  they  persist  in  a  like  course  of  slow 
poison  ;  after  a  few  generations,  the  race  becomes  extinct, — "  his 
name  even  is  cut  off  from  among  men!"     Providence  has  gifted 
man  with  reason  ;  to  his  reason,  therefore,  is  left  the  ehoice  of  his 
food  and  drink,  and  not  to  instinct,  as  among  the  lower  animals  : 
it  thus  becomes  his  duty  to  apply  his  reason  to  that  object ;  to 
shun  excess  in  quantity,  and  what  is  noxious  in  quality  ;  to  ad- 
here, in  short,  to  the  simple  and  the  natural  ;  among  which  the 
bounty  of  his  Maker  has  afforded  him  an  ample  selection  ;   and 
beyond  which  if  he  deviates,  sooner  or  later,  he  will  suffer  the 
penalty. 

Secondly.  The  view  we  have  now  taken  of  the  processes  of 
digestion,  removes  in  some  degree  that  mysterious  character  v/ith 
which  they  have  been  invested;  and  by  lessening  the  field  of  our 
inquiry,  brings  us  nearer  to  our  object.  We  had  previously  known, 
that  the  articles  employed  as  food  by  animals  are  essentially  com- 
posed of  three  or  four  elements.  But  we  have  now  learnt,  that 
all  the  more  perfect  of  those  matters  on  which  animals  subsist, 
are  compounds  of  three  or  four  proximate  principles  ;  the  whole 
of  which  compounds,  except  one,  are,  in  their  essential  charactes, 
identical  with  those  composing  the  fiameof  the  animals  themselves. 


276  CHEMISTRY  OF  ORGANIZATION. 

We  have  also  learnt,  that  owhig  to  this  identity  of  composition, 
many  animals  are  saved  the  labour  of  forming  these  proximate 
principles  from  their  elements;  and  have  only  to  re-arrange  them, 
as  their  exigencies  may  require.  The  task  of  forming  the  proxi- 
mate principles  is  thus  left  to  the  inferior  animals  or  to  plants; 
which  are  endowed  with  the  capacity  of  compounding  them  from 
matters  still  lower  than  themselves,  in  the  scale  of  organization. 
Hence  there  is  a  series,  from  the  lowest  being  that  derives  its 
nourishment  from  carbon  and  carbonic  acid,  up  to  the  most  perfect 
animal  existing.  Each  individual  in  the  series  preferring  to  assi- 
milate those  immediately  below  itself;  but  having  on  extraordinary 
occasions,  and  in  a  minor  degree,  the  power  of  assimilating  all, 
not  only  below,  but  above  itself,  in  the  system  of  organized  crea- 
tion. 

We  stated  that  the  immediate  influence  employed  by  the  organic 
agent  is  probably  galvanism,  or  the  common  agents  that  operate 
among  inorganic  matters  ;  and  that  the  digestive  apparatus,  viewed 
as  a  whole,  seems  to  be  arranged  on  galvanic  principles.  AVe 
wish,  however,  our  readers  clearly  to  understand,  that  we  con- 
sider the  organic  agent  residing  in  the  ganglionic  system  of  nerves, 
and  employing  the  electric  agency,  to  be  not  electricity  itself; 
though  the  agency  is  probably  the  lowest  kind  existing  in  animal 
bodies,  and  only,  as  it  were,  one  degree  above  the  agencies  of  in- 
animate matter.  We  dwell  on  this  point  the  more,  because  from 
deficient  recollection  of  what  electricity  is,  and  what  are  the  living 
powers  acting  through  the  nervous  system  of  animals,  it  has  been 
maintained,  nay,  has  even  been  endeavoured  to  be  experimentally 
proved,  that  these  nervous  powers  are  identical  witli  the  powers 
of  electricity.  It  is  impossible  to  imagine  a  greater  fallacy.  Ad- 
mitting that  electricity,  properly  directed,  could  change  the  proxi- 
mate elements  of  the  food  into  those  of  chyle :  can  we  imagine 
this  principle  to  vary  spontaneously  its  mode  of  operation,  so  as 
to  produce  the  same  chyle  from  every  sort  of  aliment — that  elec- 
tricity is  an  inteUigent  agency  acting  with  a  certain  object  ? 
Besides,  if  the  nervous  agency  be  identical  with  electricity,  how 
different  must  be  its  functions  in  different  nerves  ;  in  one  nerve, 
for  example,  digesting  and  assimilating  tlie  food;  in  another  con- 
veying sight ;  in  a  third  conveying  sound;  in  the  brain  itself,  shall 
we  say,  actually  thinking!  As  to  the  experiments,  on  which  it 
has  been  attempted  to  rear  this  most  untenable  opinion,  they  prove 
nothing  whatever;  and  are  easily  explained  on  other  principles. 
Sucii  explanation  would  be  foreign  to  our  present  object,  were 
we  to  introduce  it  here.  But  there  is  one  observation,  which  has 
always  appeared  to  us  conclusive  against  this  fancied  identity  of 
the  nervous  energy  with  electricity  ;  and  with  which,  we  shall 
close  what  we  have  to  offer,  regarding  the  present  subject.     Most 


ABSORPTION  OF  THE  CHYLE,  ETC.  277 

persons  are  aware  that  there  arc  certain  fishes  endowed  with  the 
power  of  evolving  electricity,  and  of  communicating  a  smart  shock 
to  other  animals.  Now,  in  all  the  fishes  in  which  this  power  re- 
sides, as  in  the  Torpedo,  there  is  a  complicated  apparatus,  extend- 
ing over  a  large  portion  of  the  fish's  body,  expressly  for  the  pur- 
pose of  forming  the  electricity,  which  the  fish  communicates  ; 
thus,  proving  beyond  a  doubt,  that  mere  nerves  are  not  suflicient 
to  develope  electricity;  and  ihat,  when  electricity  is  wanted,  aa 
express  and  peculiar  organ  is  as  requisite  for  its  secretion  or  for- 
mation, as  for  the  secretion  and  formation  of  any  other  product  of 
the  animal  economy. 

The  reflections  suggested  by  the  facts  we  have  now  detailed, 
will  be  given  in  conjunction  with  those  suggested  by  the  facts  to 
be  detailed  in  the  next  chapter. 


CHAPTER  IV. 

OF  THE  PROCESSES  OF  ASSIMILATION  SUBSEQUENT  TO  THOSE  IN  THE  STO- 
MACH AND  ALIMENTARY  CANAL  ;  PARTICULARLY  OF  THE  CONVERSION  OF 
THE  CHYLE  INTO  BLOOD.  OF  RESPIRATION,  AND  ITS  USES.  OF  SECRE- 
TION. OF  THE  FINAL  DECOMPOSITION  OF  ORGANIZED  BODIES.  GENERAL 
REFLECTIONS,  AND  CONCLUSION. 

1.  Of  the  Passage  of  the  Chyle  from  the  Alimentary  Canal 
into  the  Sanguferous  System;  and  of  the  Function  of  Absorp- 
tion generally. — The  Chyle,  as  we  have  already  said,  is  taken 
up  from  the  alimentary  canal,  by  numerous  minute  tubes,  named 
lacteals  ;  these  lubes  being  part  of  the  system  of  similar  tubes, 
which  arise  from  all  parts  of  the  body,  and  are  termed  absorbents. 
The  whole  of  the  absorbing  tubes,  after  passing  through  various 
glands,  at  length  unite  into  one  or  two  of  larger  size  ;  that  on  the 
left  side  being  by  far  the  largest,  and  known  by  the  appellation 
of  the  thoracic  duct.  These  larger  absorbent  tubes  pour  their 
contained  fluids  into  the  veins  named  the  sub-clavian  ;  and  thus 
into  the  general  mass  of  the  blood.  The  exact  nature  of  the 
changes  which  the  chyle  and  the  lymph  undergo  in  their  passage 
through  these  tubes,  is  not  well  understood.  One  change  appears 
to  be,  that  the  chyle,  as  first  formed  in  the  alimentary  canal,  is 
to  a  certain  extent,  completed^  or  freed  from  water,  during  its 
course  through  the  lacteals  :  for  though,  when  the  chyle  is  mixed 
with  the  blood,  its  albuniinous  principles  are  much  less  perfectly 
developed  than  those  of tiie  blood  itself;  yet  their  developement, 
on  their  mixture  with  the  blood,  is  more  perfect,  than  when  the 
chvle  is  first  taken  up  from  the  alimentary  canal. 

24 


278  CHEMISTRY  OF  ORGAMZATIOX. 

The  matters  conveyed  from  the  other  parts  of  the  body,  by  the 
tubes  of  the  general  absorbent  system,  have,  by  most  physiolo- 
gists, been  supposed  to  be  of  an  excrementitious  character.  That 
some  of  the  absorbed  matters  are  excrementitious,  is  very  proba- 
ble ;  arguments  may,  however,  be  adduced,  to  show,  that  the 
whole  of  ihe  matters  absorbed  are  by  no  means  excrementitious  ; 
but  that  they  are  repeatedly  consigned  to  the  uses  of  the  vital 
agency  :  every  new  organization  raising  them,  as  it  were,  a  step 
liio^her,  and  quaiifving  them  for  those   refined  and  ulterior  pur- 

o'l^^O  ••11 

poses  ;   for  which  the  crude  chyle  can  hardly  be  imagined  to  be 
at  once  adapted. 

The  circumstances  favouring  the  above  opinion,  which  we  are 
now  desirous  to  mention,  are — 

First.  It  is  unreasonable,  and  contrary  to  every  thing  we 
know  respecting  the  operations  of  the  animal  economy,  to  sup- 
pose that  the  chyle  should  be  separated  from  one  kind  of  excre- 
mentitious matter,  in  the  alimentary  canal  ;  in  order  to  be  imme- 
diately mixed  again  with  other  excrementitious  matters,  in  the 
chyliferous  tubes.  It  is,  therefore,  a  just  inference,  that  if  the 
matters  contained  in  the  absorbents  are  really  and  wholly  excre- 
mentitious, they  would  be  carefully  kept  apart  ;  and  would  be 
removed  from  the  system  by  some  other  means,  than  by  tubes 
united  with  those  conveying  the  nutritious  fluids. 

Secondly.  By  admitting  that  the  fluids  contained  in  the  absor- 
bent tubes  possess  a  highly  animalized  character,  the  design  of 
their  union  with  the  crude  and  imperfectly  animalized  chyle,  be- 
comes apparent :  the  fluid  in  the  absorbents  will  be  seen  to  exe- 
cute an  important  and  necessary  oflice  ;  by  raising  the  vital  cha- 
racter of  the  chyle,  and  qualifying  it,  for  becoming  a  part  of  the 
general  mass  of  the  blood.  We  thus  obtain  a  cogent  reason,  why 
the  fluids  taken  up  from  the  internal  surface  of  the  alimentary 
canal,  should  be  mingled  with  those  that  are  absorbed  from  other 
parts  of  the  body  ;  a  mixture  which  is  inexplicable,  on  the  hypo- 
tliesis  of  these  absorbed  fluids  being  wholly  excrementitious. 

Thirdly.  The  gradual  developement  of  the  staminal  princi- 
ples of  animal  bodies,  by  repeated  organizing  processes,  fully 
accords  with  those  general  views  of  the  operations  of  nature 
wliich,  throughout  this  work,  we  have  endeavoured  to  illustrate  ; 
and  which  lead  to  the  general  conclusion,  that  the  operations  of 
nature  are  never  abrupt,  but  always  slow  and  gradual.  Further, 
it  is  more  reasonable  to  conceive,  that  matters  already  assimilated 
to  the  animal  body,  arc  better  fitted  for  its  immediate  uses  ;  than 
those  which,  like  the  chyle,  have  only  received  an  imperfect 
assimilation. 

Fourthly.  Many  animals  can  and  do  live,  for  a  considerable 
time,  on  substances  cantained  in  their  own  bodies.  Thus  hyber- 
natlng  animals,  as  previously  stated,  have  the  ability  to  assimilate 


BLOOD.  279 

principles  of  the  blood,  gelatine  is  not  mentioned.  In  fact,  thongli 
further,  those  matters  which  have  already  become  part  of  them- 
selves ;  consequently,  such  a  faculty  of  progressive  organization 
as  we  have  supposed,  actually  exists  ;  and  a  sort  of  dif^estion  is 
carried  on  in  all  parts  of  the  body,  to  fit  for  absorption  and 
future  appropriation,  those  matters  that  have  been  already  assi- 
inilated.  Were  it  necessary,  other  arguments  to  the  same  effect 
might  be  added  :  but  we  shall  at  present  delay  t!ie  further  consi- 
deration of  the  assimilating  character  of  the  whole  absorbent  sys- 
tem ;  that  we  may  recur  to  it  again,  in  a  succeeding  part  of  the 
present  chapter. 

2.  Of  the  Blood. — The  blood  is  that  well-known  fluid  pervad- 
ing the  tubes,  named  from  their  function  the  blood-vessels  ;  which 
tubes  are  extended  more  or  less  over  every  part  of  an  animal. 
We  have  already  described  the  general  distribution  of  the  blood- 
vessels ;  and  shall  now  confine  ourselves  chiefly  to  the  properties 
of  the  blood  itself. 

The  chyle,  as  we  have  stated,  is  poured  into  the  general  mass 
of  the  blood  near  the  heart ;  and  from  the  heart  is  almost  immedi- 
ately propelled  through  the  lungs.  The  chyle,  thus  set  in  motion, 
is  not  only  united  thoroughly  with  the  blood  ;  but  undergoes  those 
other  important  changes,  by  which  its  final  conversion  into  blood 
is  accomplished.  The  exact  nature  of  these  changes  is  unknown  ; 
but  they  are  evidently  of  a  completing  character — that  is  to  say, 
the  weak  hydrated  ingredients  of  the  chyle,  are  freed  from  a  por- 
tion of  the  water  with  which  they  were  associated  ;  and  are  trans- 
muted into  the  strong  albuminous  matter  of  the  blood. 

The  chief  constituents  of  the  blood  are  essentially  albuminous. 
Blood  contains  albumen  in  three  states  of  modification  :  namely, 
albumen,  properly  so  called  ;  fibrin  ;  and  the  red  particles.  In 
addition  there  are  oily  matters  ;  besides  various  minute  portions 
of  other  animal  matters,  and  saline  matters,  all  dissolved,  or 
rather  suspended,  in  a  large  quantity  of  water.  The  following 
short  table  exhibits  the  relative  proportions  of  the  constituents  of 
human  blood  to  each  other,  as  they  exist  in  most  individuals. 

ONE  THOUSAND  PARTS  OF  HUMAN  BLOOD  CONTAIN 

Of  Water 783,37 

Fibrin              ...             -             -  2,83 

Albumen        ...             -             -  67,25 

Colouring- matters      -             -             -             -  126,31 

Fatty  matters,  in  various  states          -             -  5,16 

Various  undefined  animal  matters,  and  salts-  15,08 


1000,00* 
The  reader  will  not  fail  to  remark,  that  among  these  constituent 
*  Le  Canu  ;   mean  of  two  analyses. 


280  CHEMISTRY  OF  ORGANIZATION. 

existinff  most  abundantly  in  various  animal  structures,  s^elatlne 
is  never  found  in  the  blood,  or  in  am/  product  of  glandular  se- 
cretion. We  formerly  noticed  that  gelatine  appears  to  rank  lower 
than  albumen  in  the  scale  of  organized  substances  :  and  we  may 
now  add,  that  a  given  weight  of  gelatine,  contains  at  least  three 
or  four  per  cent,  less  carbon,  than  an  equal  weight  of  albumen. 
The  production  of  gelatine  from  albumen  must,  therefore,  be  a 
reducing  process.  VVe  shall  presently  have  occasion  to  revert  to 
these  facts.  In  the  mean  time  we  subjoin  ihe  few  observations 
we  have  to  offer,  on  the  organization  or  structure  of  the  blood. 

The  organization  of  the  blood  is  even  more  wonderful  tban  its 
chemical  composition,  and  is  still  less  understood.  The  red  por- 
tion of  the  blood,  .Hor  example,  is  composed  of  innumerable  minute 
globules,  varying  in  size  in  different  animals  ;  and  in  all  instances, 
highly  organized  :  the  real  structure  indeed  of  these  globules  is 
very  imperfectly  known  ;  but  they  are  generally  supposed  to  be 
formed  of  solid  colourless  nuclei,  within  red  vesicles.  The 
fibrin,  also,  is  diffused  through  the  mass  of  the  blood  in  a  state  of 
equally  minute  subdivision  ;  though  t!ie  particles  of  the  fibrin 
are  colourless,  and  their  magnitude  much  less  than  that  of  the  red 
particles.  From  this  inferiority  in  size,  some  physiologists  have 
been  led  to  think,  that  the  colourless  particles  of  the  Tibrin,  are 
identical  with  the  nuclei  of  the  red  particles.  During  the  life  of 
an  animal,  the  particles  of  the  fibrin,  as  well  as  the  red  particles 
of  its  blood,  seem  to  be  in  a  state  of  extreme  self-repulsion  ;  by 
which  self-repulsion,  the  union  of  these  particles  is  prevented  ; 
except  as  the  economy  of  the  animal  may  require,  and  may  de- 
termine. After  death,  however  ;  or  in  blood  withdrawn  from  the 
body  of  a  living  animal,  the  property  of  self-repulsion,  more 
especially  among  the  fibrinous  particles  of  the  blood,  ceases,  and 
they  readily  cohere  :  this  cohesion  is  termed  the  coagulation  of 
the  blood.  Much  beautiful  design  is  probably  concealed  under 
that  peculiar  organization  of  the  blood,  to  which  it  owes  its  coag- 
ulating tendency.  One  result  of  the  coagulation  of  the  blood,  in- 
deed, is  as  obvious  as  it  is  important ;  namely,  the  prevention  of 
haemorrhage.  If  the  blood  did  not  coaorulate,  the  existence  of 
animals  would  be  most  precarious  ;  as  on  the  slightest  injury,  they 
•would  be  liable  to  bleed  to  death. 

3.  Of  Respiration. — The  function  of  Respiration,  or  breath- 
ing, is  one  of  the  most  important  in  the  animal  economy,  and 
cannot,  like  many  of  the  other  functions,  be  suspended ;  the  in- 
tcrrupiion  of  that  function  being  immediately  destructive  of  life. 
When  we  described  the  phenomena  of  the  circulation  of  the  blood, 
we  observed,  that  the  blood,  in  passing  through  the  lungs,  is  ex- 
posed to  the  action  of  the  atmospheric  air.  Now,  during  this 
exposure  of  the  blood  to  the  atmospheric  air,  it  undergoes  certain 
changes.     The  blood  from  the  right  side  of  the  heart,  when  it 


RESPIRATION.  281 

enters  the  lungs,  is  of  a  dark  red  colour;  it  is  then  dispersed,  in 
a  state  of  most  minute  subdivision,  through  the  ultimate  vessels 
of  the  lungs,  and  in  these  vessels  is  brought  into  contact  with  the 
atmospheric  air,  and  becomes  of  a  bright  red  colour.  In  other 
words,  the  blood  changes  in  the  lungs  its  venous  appearance,  and 
assumes  the  character  of  arterial  blood.  The  blood  thus  arterial- 
ized,  returns  to  the  left  side  of  the  heart,  and  from  that  organ,  is 
propelled  through  the  whole  arteries  of  the  body.  In  the  minute 
terminations  of  the  arteries,  the  blood  again  loses  its  llorid  hue, 
and,  reassuming  its  dark  red  colour,  is  returned  to  the  veins,  to  the 
right  side  of  the  heart  ;  to  be  exposed  as  before  to  the  influence 
of  the  atmospheric  air,  and  to  undergo  the  same  succession  of 
chang-es. 

On  examining  the  respired  air,  a  remarkable  alteration  of  its 
properties  is  found  to  have  taken  place  ;  a  portion  of  its  oxygen 
^  has  disappeared,  and  a  similar  bulk  of  carbonic  acid  gas,  has  been 
substituted.  With  respect  to  the  origin  of  this  carbonic  acid  gas, 
there  have  been  various  opinions.  Formerly,  the  greater  number 
of  physiologists  maintained,  that  carbon,  in  some  form,  was  ex- 
creted by  the  lungs  ;  and  that  this  excreted  carbon,  uniting  with 
the  oxygen  of  the  inspired  air,  was  converted  into  carbonic  acid 
gas.  No  one  imagined  that  oxygen  gas  could  be  passing  inwards 
through  the  membrane  of  the  lungs,  while  carbonic  acid  gas  was, 
at  the  same  time,  passing  outwards,  through  the  same  membrane. 
Accurate  observations  have,  however,  demonstrated,  that  such  a 
simultaneous  passage  of  gases  really  takes  place  through  the  mem- 
brane of  the  lungs;  and  the  observations  are  not  confined  to  the 
two  gaseous  bodies  in  the  lungs  ;  but  are  applicable  to  all  gases 
whatever,  under  similar  circumstances.  In  consequence  of  these 
observations,  it  seems  now  to  be  generally  admitted,  that  the 
oxygen  of  the  atmospheric  air  is  absorbed  by  the  blood,  and,  in 
some  unknown  state  of  combination,  reaches  the  extreme  subdi- 
visions of  the  arteries  ;  where  it  is  united  with  a  portion  of  carbon, 
and  forms  carbonic  acid  gas  :  that  this  carbonic  acid  gas  is  retained 
in  some  unknown  state  of  combination  in  the  venous  blood  ;  till, 
in  the  lungs,  it  is  expelled,  and  oxygen  is  absorbed  in  its  stead ; 
according  to  the  laws  which  regulate  the  diff'usion  of  gaseous  bo- 
dies, formerly  explained.  Further,  with  the  carbonic  acid  gas, 
a  large  quantity  of  aqueous  vapour,  as  we  have  stated,  is  at  the 
same  time  separated. 

It  would  be  foreign  to  the  objects  of  this  treatise,  were  we  to 
enter  further  into  the  reasons  for  the  view  we  have  given  of  the 
phenomena  of  respiration.  These  reasons  are  many  and  strong; 
and  seem  indeed  to  prove  clearly,  that  the  changes  which  the 
blood  undergoes,  during  its  circulation  through  the  body,  are  as 
we  have  described  them.     We  shall,  therefore,  assume  that  our 

24* 


282  CHEMISTRY  OF  ORGANIZATION. 

view  of  respiration  is  correct;  and  shall  ofier  a  few  remarks  on 
the  attendant  circumstances,  and  on  the  consequences  of  respira- 
tion. 

First.  To  what  influence  are  we  to  ascribe  tlie  different  colours 
of  arterial  and  of  venous  blood  ?  The  opinion  formerly  held,  was, 
that  the  arterial  colour  arose  from  the  absorption  of  oxygen  ;  and 
the  venous  colour  from  the  presence  of  carbon.  But  recent  ob- 
servations seem  to  show  that  the  change  in  tlie  colour  of  the 
blood  during  its  circulation,  if  not  entirely  independent  of  oxygen, 
is  much  influenced  by  the  saline  matters  ;  particularly  by  the  com- 
mon salt,  wliich  the  blood  contains  :  and  that  the  dark  colour  of 
venous  blood,  is  principally  owing  to  the  presence  of  carbonic  acid 

Secondly.  What  is  the  source  of  the  carbonic  acid  in  venous 
blood,  and  of  the  aqueous  vapour  that  is  expelled  from  the  lungs  ? 
These  questions  cannot  be  answered  with  certainty.  But  some 
observations  lately  made,  have  induced  us  to  believe,  that  the 
conversion  of  albuminous  matters  into  gelatine,  is  one  great 
source  of  the  carbonic  acid  in  venous  blood.  Gelatine,  which, 
as  before  observed,  contains  three  or  four  per  cent,  less  of  carbon 
than  albumen  contains,  enters  into  the  structure  of  every  part  of 
the  animal  frame,  and  especially  of  the  skin  :  the  skin  indeed  con- 
sists of  little  else  besides  gelatine  :  it  is  most  probable,  therefore, 
that  a  large  part  of  the  carbonic  acid  of  venous  blood  is  formed  in 
the  skin,  and  in  the  analogous  textures.  Indeed,  we  know  that 
the  skin  of  many  animals  gives  off* carbonic  acid,  and  absorbs  oxy- 
gen ;  in  other  words,  performs  all  the  offices  of  the  lungs ;  a  func- 
tion of  the  skin  perfectly  intelligible,  on  the  supposition  that  near 
the  surface  of  the  body,  the  albuminous  portions  of  the  blood  are 
always  converted  into  gelatine.  With  respect  to  the  aqueous  va- 
pour thrown  off^  from  the  lungs  :  we  have  every  reason  to  believe, 
as  before  stated,  that  much  of  this  vapour  is  derived  from  the 
c/ii/le,  in  its  passage  through  these  organs  ;  and  that  by  such  se- 
paration of  water,  the  iveak  and  delicate  albumen  of  the  cliyle,  is 
converted  into  the  strong  and  perfect  albumen  of  the  blood  ;  ac- 
cording to  the  principles  detailed  at  the  commencement  of  this 
chapter. 

'I'hirdly.  What  are  the  uses  of  the  continual  extrication  of  car- 
bonic acid  from  living  animals  ;  and  could  not  a  litde  superfluous 
carbon  have  been  thrown  off"  from  their  bodies  in  a  more  simple 
manner?  The  precise  use  of  the  constant  evolution  of  carbonic 
acid,  or  how  it  is  effected,  we  know  not ;  but  one  great  use  which 
lias  been  assigned  to  this  evolution,  is,  the  formation  of  the  heat 
of  the  body  ;  and  not  only  the  power  of  forming  that  heat ;  but 
also  the  power  of  varying  it  according  to  circumstances — a  power 
so  characteristic  of  oriranized  life.     Out  of  the  bodv,  carbon  does 


SECRETION.  283 

certainly  give  off  heat  on  combination  with  oxygen.  Hence,  it 
has  been  maintained  with  great  plausibility,  that  the  same  com- 
bination, within  a  living  body,  may  give  origin  to  its  heat ;  though 
it  must  be  confessed,  that  there  are  some  difficulties  about  this 
view  of  the  origin  of  animal  heat,  which  detract  considerably  from 
its  likelihood.  Moreover,  it  is  exceedingly  probable,  that  though 
the  evolution  of  carbonic  acid  gas,  may  be  one  of  the  means  pos- 
sessed by  the  animal  economy  for  generating  heat ;  there  are  yet 
other  means,  the  nature  of  which  at  present  are  quite  unknown. 

The  quantity  of  carbon  thrown  off  by  the  lungs,  is  very  abun- 
dant ;  but  has  probably  been  much  overrated.  Philosophers  have, 
for  instance,  calculated  that  the  lungs  of  a  man  of  ordinary  size 
expel,  in  the  course  of  twenty-four  hours,  eleven  ounces  of  car- 
bon ;  a  quantity  more  than  equal  to  that  contained  in  six  pounds 
of  beef.*  If  carbon  be  indeed  thrown  off  from  the  lungs  so  co- 
piously; it  must  be  produced  within  the  body.  It  is  difficult  to 
account  for  the  quantity  of  carbon  thrown  off,  even  on  the  lowest 
estimate.  We  are,  therefore,  necessarily  obliged  to  conclude,  that 
more  solid  matter  is  every  day  expelled  from  the  body  by  the 
lungs,  than  in  any  other  manner.  Hence  the  probability  of  the 
opinion  formerly  noticed,  that  the  matters  taken  up  by  the  absor- 
bents, and  by  the  veins,  enter  successively  into  the  formation  of 
various  parts  of  the  animal  frame  ;  instead  of  being  removed,  im- 
mediately after  their  absorption,  as  at  present  is  generally  sup- 
posed. For  it  seems  hardly  possible  to  reconcile,  with  the  quan- 
tity of  food,  the  great  quantity  of  carbon  that  is  expelled  from  the 
lungs  alone  ;  much  less,  what  must  be  expelled  if  all  the  matter 
taken  up  by  the  absorbents  be  likewise  considered  excrementitious. 

4.  Of  Secretion. — From  the  blood,  are  formed,  by  means  of 
peculiar  apparatus,  all  those  numerous  products  termed  Secre- 
tions ;  not  only  so  unlike  each  other,  but  so  unlike  the  fluid 
from  which  they  are  originally  separated.  Some  of  these  se- 
creted products  appear  to  be  little  else,  than  a  separation  of  cer- 
tain matters  already  existing  in  the  blood.  Other  secretions  have 
no  resemblance  to  any  ingredient  of  the  blood  :  consequently,  in 
the  glandular  structure,  by  which  these  secretions,  so  dissimilar 
to  the  blood,  are  formed,  the  blood  must  undergo  some  essential 
change.  In  the  present  state  of  our  information,  however,  we 
must  content  ourselves  with  a  limited  insight  into  the  nature  and 

*  According'  to  an  elaborate  analysis,  by  Berzelius,  the  muscle  of  an  ani- 
mal contains  77  per  cent,  of  water,  and  23  per  cent,  of  other  matters. 
Supposing-,  what  is  near  the  truth,  that  22  of  these  23  parts  consist  of  al- 
bumen, and  that  this  albumen  contains  half  its  weight  of  carbon  ;  which  in 
round  numbers  is  a  sufficiently  neat  approximation  ;  it  foUowa,  that  100 
parts  of  the  muscular  fibre  of  animals,  contain  about  11  parts  of  carbon  ; 
so  that  11  ounces  of  carbon  must  represent  100  ounces  of  beef;  that  is, 
upwards  of  six  pounds  as  stated  in  the  text. 


284  CHEMISTRY  OF  ORGANIZATION. 

the  pauses  of  secretory  action.  We  see  that  secreted  products 
are  of  two  kinds  ;  that  some  of  the  maiters  separated  by  animal 
bodies  are  evidendy  thrown  oft',  on  account  of  their  noxious  quali- 
ties;  are,  in  fact,  excretions  ;  which  could  not  be  retained  with- 
out proving  fatal  to  the  life  of  the  animal  from  which  they  are 
detaclied  :  while  others  again,  are  as  obviously  intended  for  furtlier 
objects,  and  for  the  performance  of  various  subordinate  actions  in 
the  living  system  ;  are  in  fact,  secretions  ;  properly  so  called.  But 
as  we  have  stated,  we  are  still  perfecdy  unacquainted  with  the 
intimate  nature  of  these  changes  ;  though  it  is  probable  that  a 
careful  examination  of  the  phenomena,  would  throw  much  light 
on  their  general  character ;  and  display  evidence  of  the  most 
consummate  design. 

5.  Spontaneous  decciy  of  Organized  Bodies. — It  remains 
finally  to  ch)se  this  work  with  a  few  observations  on  the  sponta- 
neous, and  inevitable  decay,  of  all  those  things  that  are  produced 
by  organization;  after  they  have  been  removed  from  the  influence 
of  the  organic  agents,  by  which  the  combination  of  their  consti- 
tuent principles  was  eflTected. 

The  organized  beings  that  inhabit  this  globe,  however  nume- 
rous, have  a  very  small  relation  to  the  magnitude  of  the  globe, 
and  seem  to  occupy  its  surface  only.  We  have  seen  that  the  ele- 
ments forming  the  structure  of  these  beings,  are  not  only  com- 
bined in  diilereiU  proportions,  but  that  they  appear,  in  many  in- 
stances, to  undergo  further  decomposition  into  ultimate  forms  of 
matter,  which,  out  of  a  living  body  do  not,  and  perhaps,  in  the 
present  constitution  of  the  universe,  cannot,  exist  in  an  isolated 
state.  Owing  to  this  diversity  in  the  composition  of  organized 
beuisfs  from  that  of  inoro^anic  matter,  and  to  other  causes  which 
will  readily  occur  to  the  reader,  organized  beings  and  their  laws, 
are  in  continual  opposition  to  the  general  laws,  by  which  inor- 
ganic matter  is  governed.  To  counteract,  therefore,  these  oppo- 
site laws,  and  to  maintain  the  existence  of  organized  beings, 
recjuire  the  unremitting  eflbrts  of  the  organic  agency.  But  at  length 
these  efforts  are  exhausted  ;  the  contest  ceases  ;  when  the  gene- 
ral laws  of  inorganic  nature  prevail,  and  speedily  reduce,  to  their 
original  stale  of  existence,  the  atoms  which  had  been  incarce- 
rated in  the  living  frame. 

The  spontaneous  decay  of  organized  beings  is  usually  termed 
the  putrefactive  process  ;  and  some  substances  are  much  more 
prone  than  others,  to  undergo  that  change.  As  miglit  be  ex- 
pected ;  those  substances  whose  constitution  is  most  simple,  as 
the  oils,  and  Ixxhes  of  a  like  nature,  are  also  the  most  permanent; 
■wliile  sul).si;inces  more  compounded,  especially  those  which  in- 
clude azote,  are  exceedingly  liable  to  putrescent  change.  For 
such  changes  a  certain  degree  of  heat  and  of  moisture  appear  to 


RECAPITULATION  AND  REFLECTIONS.  285 

be  necessary :  since  in  a  temperature  below  the  freezing  point  of 
water,  or  in  a  perfectly  dry  state  of  the  atmosphere,  even  animal 
substances  njay  be  preserved  uiichan<.{ed  (hiring  any  length  of  time. 
The  ]>henomena  attending  the  dissoluiion  of  different  kinds  of  or- 
ganized matters  are  of  course  dill'erent ;  but  in  every  instance,  the 
tendency  is  toward  the  formation  of  compounds  more  simple 
than  the  matter  decomposed  ;  that  is  to  say,  of  compounds  whose 
existence,  out  of  a  living  body,  is  not  incompatible  with  the  pre- 
sent state  of  the  globe.  Those  matters  which,  in  a  warm  and  damp 
air,  seem  first  to  be  loosened  from  organic  combination,  are  those 
foreign  bodies  we  formerly  mentioned,  as  existing,  in  every  part 
of  the  structure  of  organized  beings,  in  some  unknown  but  active 
self-repulsive  state.  Hence,  during  putrescent  action,  arises  the 
formation  of  sulphuretted  and  phosphoretted  hydrogen,  and  of  other 
undefined  compounds  of  the  same  elements:  and  these  gaseous 
compounds,  chiefly,  produce  the  very  offensive  odour  of  putre- 
faction. At  the  same  time,  there  are  formed,  carburetted  hydro- 
gen, oil,  acetic  acid,  ammonia,  and  last  of  all,  carbonic  acid  gas 
and  water;  while  the  azote  is  extricated  in  a  gaseous  condition. 
Finally,  both  vegetable  and  animal  matters,  but  vegetable  matters 
more  especially,  are  reduced  to  the  state  of  mould.  The  mould 
from  vegetable  matters,  consists  principally  of  carbon,  in  combi- 
nation with  a  Hide  oxygen  or  hydrogen  :  the  mould  from  animal 
products,  consists  of  similar  matters,  mixed  with  a  litde  azote, 
and  the  usual  saline  ingredients  of  organized  substances.  In  this 
form  of  mould,  the  remains  of  vegetables  and  of  animals,  as  was 
before  stated,  constitute  the  food  of  plants  ;  by  which  they  are 
again  organized,  and  thus  go  through  the  same  series  of  changes. 

We  may  here  pause  for  a  moment,  and,  on  account  of  the  ge- 
neral reader,  briefly  recapitulate  the  most  striking  facts,  that  iiave 
been  detailed  in  the  present,  and  in  the  preceding  chapters. 

In  the  first  place,  the  mcchanicMl  arrcmgcmtnts  for  reducing 
the  food  of  animals  to  the  proper  degree  of  comminution,  are 
wonderfully  varied,  according  to  the  peculiar  qualities  of  that  food. 
In  the  graminivorous  and  granivorous  tribes,  for  example,  the 
teeth  are  literally  instruments  for  grinding  or  triturating  herbaceous 
matters,  and  seeds.  In  carnivorous  animals,  such  a  structure  * 
would  be  useless  :  the  teeth,  therefore,  are  suited  only  for  cutting, 
or  tearing.  In  knawing  animals,  the  teeth  present  a  totally  differ- 
ent structure,  but  at  the  same  time  are  admirably  fitted  to  the  ha- 
bits of  the  animal.  Occasionally,  as  in  the  fowl  trihe  of  birds, 
the  grinding  apparatus  is  placed,  not  in  the  mouth,  but  in  the 
stomach  itself;  this  organ  being,  as  it  were,  expressly  contrived 
for  trituration  ;  while  some  of  the  functions  it  performs  in  other 
animals,  are  transferred  to  contiguous  parts. 

The  structure  and  mechanism  of  the  stomach,  and  of  the  all- 


286  CHEMISTRY  OF  ORGANIZATION*. 

mentary  canal,  then  claim  our  particular  attention.  In  carnivorous 
animals,  whose  food  requires  comparatively  little  assimilation, 
the  alimentary  canal  is  short,  and  of  a  simple  structure.  On  the 
other  hand,  in  vegetable  feedets,  that  canal  is  long  and  compli- 
cated ;  but  perfectly  adapted  for  macerating  their  food,  and  f(U" 
extracting  from  it,  everything  that  can  be  converted  into  nourish- 
ment. Nor  is  there  an  adherence  to  any  model,  but  the  whole 
is  throughout  varied  ;  as  if  in  order  to  demonstrate  the  power  and 
the  wisdom  of  llim  by  whom  they  were  contrived.  Thus  the 
alimentary  canals  of  the  cow,  and  of  the  horse,  are  formed  on  en- 
tirely different  models  ;  though  the  food  of  both  animals  be  nearly 
the  same. 

We  proceed  in  the  next  place,  to  the  consideration  of  the  che- 
mical changes,  which  the  food  undergoes  in  the  stomach  and 
duodenum.  In  these  chano-es  we  discover  arrangements  not  less 
wonderful,  indeed  more  wonderful,  than  in  those  of  structure  and 
of  mechanism.  The  variety  of  forms,  assumed  by  bodies  having 
the  same  essential  composition,  produces  a  latitude,  in  the  choice 
of  diet,  which  is  almost  infinite  :  at  the  same  time,  the  organs  being 
endowed  with  the  power  to  discriminate  all  these  differences,  and 
to  act  on  the  ultimate  principles  of  bodies  ;  elaborate,  from  all 
these  various  forms  of  matter,  the  same  uniform  resulting  chyle. 
The  povver  by  which  the  stomach  is  enabled  to  effect  these  asto- 
nishing changes,  is  the  power  which  it  possesses,  of  associating 
the  different  alimentary  substances  with  water;  the  power,  in 
sliort,  of  dissolving  or  digesting  them.  This  dissolving  power 
seems  to  be  exerted  through  the  agency  of  chlorine,  derived  from 
the  common  salt  in  the  blood;  at  least,  chlorine  is  always  present 
in  the  stomach,  during  the  act  of  the  solution  of  the  food  ;  though 
the  precise  mode  in  which  it  operates,  is  stdl  unknown.  Con- 
tem})oraneously  with  the  act  of  solution  of  the  food,  such  essen- 
tial changes  take  place  in  its  composition,  as  are  requisite  for 
perfecting  the  fviture  chyle. 

'J'iie  stomach  having  accomplished  its  office,  the  digested  mass 
enters  the  duodenum  ;  where  the  scries  of  chanffes  is  continued 
in  a  manner  equally  wonderful.  In  the  duodenum,  the  digested 
mass  is  brought  in  contact  with  the  biliary  and  the  pancreatic 
fluids.  The  alkali  of  the  bile  unites  with  the  acid,  with  which 
the  food  had  been  mingled  during  its  digestion  in  the  stomach; 
the  excrementitious  parts,  both  of  the  food,  and  of  the  bile,  are 
separated  or  precipitated  ;  while  at  the  same  time,  the  proper 
chylous  princi[)les  are  eliminated,  in  a  condition  appropriate  for 
their  absorption  by  the  lacteals. 

'IMiere  are  two  divisions  of  those  minute  tubes,  that  compose 
what  is  termed  the  absorbent  system  of  animals  ; — the  lacteals — 
and  the  absorbents  properly  so  called.  The  ultimate  ramifications 
of  the  lacteals,  originate  from  the  internal  surface  of  the  alimcn- 


RECAPITULATION  AND  REFLECTIONS.  287 

tary  canal,  M^here  they  take  up  the  digested,  and  partly  assimilated, 
element  or  chyle.  The  ultimate  ramifications  of  the  proper  absor- 
bents, originate  from  all  parts  of  the  body  ;  and  are  enabled  to 
take  up,  by  some  peculiar  process,  every  component  of  the  body, 
solid  as  well  as  fluid,  in  the  same  manner  as  the  chyle  is  taken 
up  by  the  lacteals. 

Tlie  fluid  obtained  from  the  lacteals,  and  that  obtained  from  the 
proper  absorbents,  are  both  alike  albuminous.  Tiie  albumen  of 
the  chyle,  as  we  have  formerly  shown,  is  produced  in  the  stomach 
and  duodenum,  while  the  food  is  undergoing  the  process  of 
digestion.  But  whence  is  the  albumen  derived,  that  is  found  in 
the  proper  absorbents  ?  The  animal  body  we  know  to  be  com- 
posed of  a  great  variety  of  matters,  among  which  gelatine  pre- 
dominates. Now,  since  albumen  only  is  found  in  the  absorbents, 
it  follows,  that  before  the  gelatine  of  the  body  is  taken  up  by  the 
absorbents,  it  is  re-converted  into  albumen  :  in  other  words,  the 
absorbed  gelatine  undergoes  a  process,  entirely  analogous  to  that 
which  gelatine,  and  other  matters,  undergo  in  the  stomach  and 
duodenum,  during  the  process  of  digestion.  Hence,  the  diges- 
tive process,  instead  of  being  confined  to  the  stomach  and  duode- 
num, is  actually  carried  on  without  intermission,  in  all  parts  of  a 
living  animal  body. 

The  two  kinds  of  fluid  albumen  derived  from  these  two  sources; 
that  is  to  say,  the  crude  chyle  in  the  lacteals,  and  the  highly 
animalized  lymph  in  the  absorbents,  are  at  length  commingled; 
and  form  one  uniform  fluid  of  an  intermediate  character,  adapted 
for  becoming  a  part  of  the  general  mass  of  the  blood.  The  cha- 
racter however  of  this  fluid,  when  it  becomes  part  of  the  blood, 
though  albuminous,  is  still  very  weak  ;  that  is  to  say,  the  fluid 
consists  of  albumen,  holding  a  large  proportion  of  water  in  a 
stale  of  essential  combination.  By  a  beautiful  arrangement,  as 
soon  as  this  weak  albuminous  fluid  is  mingled  with  the  blood,  it 
is  hurried  through  the  lungs  ;  where  it  undergoes  a  remarkable 
change.  In  the  lungs,  the  water,  which  is  in  essential  union 
with  the  weak  albuminous  matter  of  the  chyle,  is  separated  and 
expelled  along  with  the  carbonic  acid  gas,  which  is  continually 
escaping  from  these  organs  ;  and  at  the  same  lime,  the  weak 
and  delicate  albuminous  matter  of  the  chyle,  is  converted  into  the 
strong  and  firm  albuminous  matter  of  the  blood.  We  are  thus 
brought  to  consider  the  process  of  respiration. 

The  blood,  in  its  course  through  the  lungs,  emits  carbonic  acid 
gas,  and  assumes  a  florid  arterial  colour.  At  the  same  time,  ac- 
cording to  the  principles  of  gaseous  diffusion,  the  blood  absorbs, 
in  the  lungs,  a  portion  of  oxygen  from  the  air  of  the  atmosphere. 
The  oxygen  thus  absorbed,  remains  in  some  peculiar  state  of 
union  witli  the  blood,  (Query,  as  oxygenated  water,  or  some 
analogous  compound  ?)  till  the  blood  reaches  the  ultimate  termi- 


288  CHEMISTRY  OF  ORGANIZATION. 

nations  of  the  arteries.  In  these  minute  tubes  the  oxygen  changes 
its  mode  of  union;  it  com.bines  with  a  portion  of  carbon,  and  is 
converted  into  carbonic  acid  ;  which  carbon  must  be  derived  from 
the  albuminous  principles  of  the  blood.  Two  distinct  alterations 
take  place  during  the  union  of  the  carbon  with  the  oxygen  :  a 
portion  of  the  albumen  contained  in  the  blood  is  sujiposed  to  be 
reduced  to  the  state  of  gelatine  ;  w^hich  gelatine  is  appropriated 
toward  the  renovation  of  those  textures  wliose  composition  is 
chiclly  gelatinous  :  at  tlie  same  time,  the  carbonic  acid  which 
had  been  formed  from  t!ie  reduced  albumen,  nnites  with  the  blood, 
communicates  to  that  fluid  its  dark  venous  colour,  and  is  trans- 
ferred to  the  lungs  ;  where  it  is  expelled  from  the  system,  along 
with  a  portion  of  aqueous  vapour,  derived  principally  from  the 
weak  albumen  of  the  chyle  ;  as  formerly  explained. 

The  blood  is  the  source,  not  only  of  all  the  constituent  princi- 
ples of  animal  bodies,  but  likewise  of  all  the  various  secretions  ; 
many  of  which  difler  altogether,  in  their  properties,  from  those 
of  llie  primary  fluids,  and  perform  secondary  offices,  of  great  im- 
portance in  the  animal  economy.  Other  products  separated  from 
the  blood,  are  purely  excretions;  as,  for  instance,  the  carbonic 
acid  gas  from  the  lungs  ;  which  could  not  be  retained  in  the  ani- 
mal system  without  destroying  life. 

Finally,  the  life  of  the  animal  becoming  extinct,  the  essential 
properties  of  the  matter  of  which  it  is  composed,  resume  their 
natural  action,  and  speedily  restore  the  elements  to  their  original 
condition. 

Sucli  is  a  summary  of  those  operations  of  living  bodies,  which, 
in  the  present  and  in  the  preceding  chapters,  we  have  endeavoured 
to  illustrate  ;  and  though  our  insight  into  those  operations  be 
ver}^  imperfect,  it  is  amply  sutficient  to  satisfy  us,  of  the  infinite 
wisdom  by  which  they  are  directed  ;  and  that  the  unknown,  must 
be  far  more  wonderful  than  what  has  been  disclosed.  Most  of 
the  facts  on  which  we  have  dwelt,  are  of  a  character  so  obvious, 
that  they  require  only  to  be  understood,  in  order  to  be  admitted 
among  the  proofs  of  the  great  argument  of  design  ;  at  least,  by  all, 
but  those  who  alTect  to  deny  that  argument.  We  therefore  leave 
to  the  reader,  the  application  of  facts,  so  obviously  demonstrative 
of  design  ;  and  proceed  to  ofi'or  a  few  remarks  on  certain  general 
arrangements  of  organized  and  living  beings,  relatively  to  those 
of  inorganic  matter. 

First.  In  considering  the  economy  of  organized  beings,  one  of 
the  circumstances  most  calculated  to  arrest  our  attention,  is  the 
cxtraordiuiiry  skill  manifested  in  the  disposal  of  the  various  parts 
of  the  organized  system,  with  regard  to  each  other.  As  an  in- 
stance, on  the  great  scale,  may  be  noticed,  the  mutual  relation 
and  dependance  of  plants  and  animals.  Thus,  as  we  formerly 
pointed  out,  carbonic  acid  gas  constitutes  the  chief  food  of  plants; 


RECAPITULATION  AND  REFLECTIONS.  289 

and  we  now  see,  that  nearly  the  whole  of  the  superfluous  carbon 
produced  by  the  operations  of  the  animal  system,  is  actually 
thrown  off  in  the  form  of  carbonic  acid.  Plants,  therefore,  on 
the  one  hand,  supply  the  chief  nourishment  to  animals  ;  while 
that  gaseous  matter  which  is  separated  by  the  animal  economy, 
and  which  if  retained  within  animals,  would  to  them  be  fatal, 
constitutes,  on  the  other  hand,  the  chief  food  of  plants.  Nor  in 
these  two  respects  only,  are  the  two  great  systems  of  organiza- 
tion mutually  dependent ;  for  unless  plants  consumed  the  carbonic 
acid  gas  which  is  formed  by  animals  ;  this  deleterious  compound 
would  probably  accumulate  in  the  atmosphere,  so  as  to  destroy 
animal  life  ;  while  it  is  doubtful,  whether  the  present  races  of 
vegetables  could  exist,  if  carbonic  acid  gas  were  not  formed 
by  animals.  Again,  the  general  scheme  of  Providence,  for  the 
nourishment  of  animals,  claims  our  especial  notice.  Animals 
have  not  only  been  destined  to  prey  on  each  other  :  but  all  created 
beings  are  the  food  of  those  progressively  higher  than  themselves, 
in  the  scale  of  organization.  By  this  wise  arrangement,  the 
labour  of  the  assimilating  power  has  been  greatly  diminished  ; 
and  by  the  same  means,  that  accumulation  of  dead  animal  re- 
mains which  soon  would  be  overwhelming,  is  entirely  prevented. 
Even  in  the  fabric  of  individual  animals,  and  in  the  operations 
carried  on  within  them,  the  same  wise  purposes  of  mutual  rela- 
tion and  dependance  are  observable.  Thus,  whether  we  contem- 
plate the  repeated  employment  of  the  same  materials  ;  or  the 
various  important  ends,  in  many  instances  accomplished  by  the 
same  process  ;  we  discover,  throughout,  the  utmost  abridgement 
of  labour  ;  so  that  the  greatest  possible  effect,  is  every  where 
produced,  by  the  simplest  possible  means. 

Secondly.  The  general  subserviency,  of  the  mechanical  ar- 
rangements of  the  frame  of  organized  beings,  to  the  chemical  ope- 
rations that  are  carried  on  within  them,  is  of  still  greater  interest 
and  importance,  than  even  those  arrangements  have  been  shown 
to  be.  Wemay  view  an  organized  being  as  a  piece  of  intricate 
machinery,  adapted  to  the  physical,  and  the  chemical  properties 
of  matter.  The  adaptation  of  this  machinery  to  the  physical  pro- 
perties of  matter,  belongs  to  another  department.  Our  attention 
is  directed  solely  to  the  chemical  adaptations.  The  performance 
of  the  chemical  changes  within  organized  beings,  through  the  in- 
terposition of  mechanical  arrangements,  as  has  been  stated  in  a 
former  part  of  this  work,  establishes,  beyond  a  doubt,  that  these 
chemical  changes  have  a  real  existence.  Thus,  when  we  wit- 
ness such  a  display  of  elaborate  arrangements,  as  are  exhibited  in 
the  mechanism  of  the  digestive  organs,  and  of  the  circulating 
system  ;  the  purpose  of  which  arrangements  is  merely  to  produce 
a  few  chemical  changes  in  the  food,  and  in  the  blood  ;  it  is  evi- 

25 


290  CHEMISTRY  OF  ORGANIZATION. 

dent  that  the  chemical  changes  so  produced,  must  be  at  least  as 
real,  as  the  mechanical  structure,  by  means  of  which  they  are  ef- 
fected. Hence  the  adaptations  of  mechanical  arrangements,  in 
the  structure  of  organized  beings,  to  the  pre-existing  chemical 
properties  of  matter,  affords  an  evidence  of  design,  not  less  im- 
pressive than  unequivocal.  The  most  determined  sceptic  can- 
not assert  that  there  is  any  necessary  relation,  or  indeed  any  re- 
lation whatever,  between  the  mechanical  arrangements,  and  the 
chemical  properties  to  which  they  administer.  There  is  no  rea- 
son why  the  chemical  changes  of  organization,  should  result  from 
the  mechanical  arrangements,  by  which  they  are  accomplished  : 
neither  is  there  the  slightest  reason,  why  the  mechanical  arrange- 
ments in  the  formation  of  organized  beings,  should  lead  to  the 
chemical  changes  of  which  they  are  the  instruments.  From  what 
cause,  then,  arose  the  association  of  the  chemical  changes  with 
the  mechanical  arrangements  ?  How  were  the  chemical  opera- 
tions of  digestion  and  of  respiration  brought  into  union  with  the 
mechanical  apparatus  of  digestion,  and  with  the  circulating  sys- 
tem ?  The  co-existence  of  things  so  entirely  dissimilar,  and  hav- 
ing no  kind  of  mutual  relation,  can  be  explained  only  on  the  sup- 
position that  a  ivill  exists  somewhere  ;  and  also  3.  jwiver  to  exe- 
cute that  ivill.  The  existence  is  thus  unavoidably  acknowledged 
of  a  Being,  who  knowing  every  pre-existing  chemical  property  of 
matter,  and  willing  to  direct  these  properties  to  a  specific  object, 
has  contrived  for  that  purpose  an  apparatus  admirably  fitted  to 
attain  His  object.  Such  is  the  explanation — the  only  possible 
explanation,  of  the  subserviency  of  mechanism  to  chemistry,  in 
the  processes  of  organic  life.  And  what  is  this  explanation,  but 
our  argument  of  design,  in  terms  that  seem  absolutely  irresisti- 
ble ? 

Thirdly.  That  perpetual  renovation  and  decay  to  which  all  or- 
ganized beings  arc  liable,  may  be  considered  as  a  part  only  of  the 
great  round  of  changes,  which  we  witness  in  everything  that  has 
been  created.  The  world  itself,  as  we  have  seen,  appears  to 
have  been,  at  intervals,  subjected  to  changes  involving  even  the 
fundamental  laws  by  which  it  is  governed.  Nothing,  therefore, 
belonging  to  the  world,  can  reasonably  be  expected  to  be  perma- 
nent. Had  there  been  even  an  approach  to  such  permanence,  the 
beautiful  adaptations  of  organized  beings  to  the  pre-established  laws 
of  inanimate  matter,  and  all  the  other  wonderful  arrangements  we 
have  described,  could  not  have  been  manifested  as  they  now  are. 
Besides,  to  the  changes  we  ourselves  undergo,  we  are  nidebted  for 
the  greater  part  of  the  enjoyments  of  our  life.  If  none  died,  none 
could  be  born  ;  and  the  present  arrangements  of  human  society 
could  have  no  existence.  There  would  be  none  of  the  pleasing 
relations  of  parent  and  offspring ;  none  of  the  agreeable  variety  of 
childhood,  of  youth,  of  maturity,   and  of  age,  experienced  by 


RECAPITULATION  AND  REFLECTIONS.  291 

every  individual ;  which,  with  all  the  other  numerous  relations 
of  society,  incidental  to  the  persons  of  different  individuals,  con- 
tribute so  largely  to  human  happiness.  Were  man  exempt  from 
change  ;  whether  the  rest  of  the  world  were  supposed  to  be  pro- 
gressive, as  it  is  ;  or  whether  it  were  stationary,  as  regards  him  ; 
the  same  uniform  and  dull  monotony  would  prevail,  the  same 
want  of  motive.  In  short,  with  our  present  constitution  and  feel- 
ings, perpetuity  and  uniformity  would  be  physically  and  morally 
impossible. 

But  why,  it  has  a  thousand  times  been  asked,  why  has  the 
world  been  so  constituted  ?  AV-hy  this  unceasing  round  of  change  ? 
Whence  its  origin?  AVhat  its  object? — Such  questions,  the 
Great  Author  of  the  universe  alone  can  answer.  But  as  within 
those  narrow  limits  by  which  our  observations  are  bounded, 
wherever  we  can  trace  His  desii^ns,  we  see  that  His  works  are 
never  without  an  object ;  we  cannot  doubt  that  in  determining 
their  perpetual  change,  there  is  no  less  an  object ;  though  it  be 
above  our  comprehension.  By  placing  immaterial  and  intelligent 
beings,  for  a  time,  in  personal  connection  with  matter,  He  has 
indeed  communicated  to  them  a  knowledge  of  those  properties  of 
matter  which  so  strikingly  display  His  wisdom  and  power;  and 
this  may  have  been  one  of  His  objects  :~but  to  speculate  further 
on  points  so  utterly  beyond  our  capacity,  would  be  presumptuous  : 
for  who  can  "know  the  mind  of  God,  or  who  hath  been  His 
counsellor  ?" 


We  have  thus  given  a  brief  outline  of  what  has  been  denomi- 
nated the  Chemistry  of  organization  ;  in  other  words,  an  account 
of  those  changes  and  combinations  which,  through  the  operation 
and.  the  agencies  of  inorganic  matter,  organic  agents  are  capable 
of  effecting.  The  information  it  has  been  in  our  power  to  give, 
though  imperfect,  we  have  shown  to  be  amply  sufficient,  not  only 
to  demonstrate  the  astonishing  wisdom,  and  foresight,  with  which 
organized  beings,  in  as  far  as  we  can  understand  them,  have  been 
contrived  and  formed  ;  but  the  infinitely  higher  perfection  of  both 
these  attributes,  requisite  to  impart  to  organization  that  vitality, 
the  nature  of  which  so  entn*ely  surpasses  our  conception'. 

We  shall  now  close  this  volume  with  a  few  observations  on 
the  future  progress  of  chemistry  ;  on  the  means  by  which  this 
science  may  be  applied  to  physiological  research  ;  and  on  the 
tendency  of  physical  knowledge  in  general. 

Chemistry,  as  we  pointed  out  in  the  introduction  to  this  treatise, 
forms  the  connecting  link  between  those  branches  of  human 
knowledge  which  are  founded  on  quantity,  and  those  which  are 
derived  solely  from  experience.  All  our  experimental  knowledge 
that  is  not  chemical  ;  for  instance,  all  that  physiology  which  re- 


292  CHEMISTRY  OF  ORGANIZATION. 

lates  to  the  phenomena  of  life,  is  wholly  removed  from  the  logic 
of  quantity,  and  depends  entirely  on  observation.  Now  so  far  as 
the  logic  of  quantity  is  applicable,  so  far  are  we  certain  of  our 
conclusions,  as  certain  at  least  as  we  are  of  our  own  existence,  or 
that  we  see  and  hear.  But  when  this  logic  cannot  be  applied, 
our  conclusions  are  no  longer  such  as  imist  be — no  longer  follow 
from  our  premises  a  necessary  consequence  ;  but  are  only,  for  the 
most  part,  such  as  may  be  ;  that  is  to  say,  have  no  more  than 
that  degree  of  probability  which  arises  from  the  evidence  we  have 
of  the  truth  of  the  phenomena  or  events,  forming  our  premises. 

In  all  knowledge  depending  on  mere  observation  or  experiment, 
what  we  know,  is  grounded  on  our  own  observation  and  experi- 
ence, or  on  the  observation  and  experience  of  others.  What 
we  ourselves  observe,  we  too  often  observe  very  imperfectly;  or 
do  not  understand,  wdien  observed.  But  phenomena  or  events, 
the  knowledge  of  which  we  are  obliged  to  receive  at  second  hand, 
on  the  testimony  of  others  ;  and  which  may  have  been  observed 
through  the  distorted  medium  of  ignorance  or  of  prejudice — may 
even  have  been  wilfully  misrepresented — of  these  we  have  a  still 
less  assurance.  If  a  phenomena  or  event  has  happened  only  once, 
and  be  therefore  historical;  we  are  under  the  necessity  of  acquies- 
cing in  its  truth,  or  of  estimating  its  probability,  according  to  the 
rules  of  evidence.  If  the  phenomenon  or  event  be  of  frequent  oc- 
currence, or  if  its  nature  be  such,  that  it  is  capable  of  being  brought 
under  our  own  observation ;  in  order  to  remove  our  uncertainty, 
we  endeavour  to  observe  it  ourselves  ;  in  short,  we  make  an  ex- 
periment. Such  is  the  method  we  pursue,  in  obtaining  all  that 
knowledge  which  is  the  result  of  mere  observation.  The  differ- 
ent events  succeed  one  another,  but  we  know  not  wherefore ;  we 
see  not  their  mutual  connexion.  We  believe  that  an  event  will, 
probably,  follow  another  event ;  because  the  one  event  has  always 
followed  the  other,  or  because  of  some  other  probability  ;  but  we 
cannot  discover  that  7iecc55o?'?/  connexion  between  the  two  events, 
which  so  irresistibly  leads  us  to  determinate  conclusions,  where 
we  can  apply  the  laws  of  quantity. 

The  foregoing  remarks  may  be  viewed  as  a  continuation  of 
those  offered  in  the  introduction  to  this  volume,  and  chiefly  relate 
to  the  progress  of  chemistry.  Chemistry  being  a  science  of  ob- 
servation, we  can  form  but  a  very  imperfect  conception  of  its  fu- 
ture progress;  because,  we  cannot,  by  reasoning,  anticipate  the 
discovery  of  those  chemical  facts  which  are  yet  concealed.  The 
progress  that  chemistry,  within  these  k\v  years,  has  made,  is  truly 
astonishing  ;  and  when  a  more  rigorous  mode  of  observation  shall 
be  adopted — in  short,  when  chemistry  shall  be  brought  more  under 
the  control  of  the  laws  of  quantity — a  control  that  will  be  exer- 


CONCLUSION.  293 

cised,  at  least  indirectly — it  is  impossible  to  foretell  the  degree  of 
perfection  which  chemistry,  as  a  science,  may  attain.  But,  for 
many  years  yet  to  come,  the  progress  of  chemistry  must  depend 
solely  on  experiment ;  and  its  cultivators  must  be  satisfied  with 
the  comparatively  humble  oflice,  of  discovering  the  actual  chemi- 
cal changes,  which  bodies  effect  on  each  other. 

Since,  then,  in  knowledge  derived  from  observation,  an  acquaint- 
ance with  what  exists,  and  with  ivhat  is  done,  is  indispensable ; 
to  obtain  a  clear,  accurate,  and  unequivocal  conception  of  these 
things,  is  the  first  duty  of  every  observer,  and  of  every  experimen- 
talist. Nor  is  there  any  observer,  or  experimentalist,  however 
unpretending,  who  may  not  add  to  the  stock  of  ascertained  facts  ; 
so  varied  and  inexhaustible  are  the  stores  of  nature.  Another  duty 
of  every  one  who  engages  in  observation  or  experiment,  is  to  be- 
come the  faithful  historian  of  what  he  witnesses  ;  to  narrate  the 
event  or  phenomenon  in  plain  and  intelligible  language,  employ- 
ing only  terms  of  a  definite  meaning ;  so  as  to  convey  to  others  a 
just  notion  of  what  he  has  seen.  We  say  a  just  notion;  in  the 
greater  number  of  instances,  a  perfect  notion  is  impossible  ;  be- 
cause what  is  seen,  cannot  be  expressed  by  language.  But  to  give 
a  just  notion  ;  that  is  to  say,  a  notion  which,  though  incomplete, 
has  710  foreign  or  false  gloss,  is  within  the  power  of  every  ob- 
server ;  and  to  give  such  a  notion  of  the  facts  he  narrates,  ought 
to  be  his  chief  study.  One  testimony  of  so  faithful  a  witness  is 
often  invaluable,  and  worth  a  thousand  vague  and  inaccurate  ob- 
servations ;  which  are  only  calculated  to  bewilder,  or  to  mislead ; 
and  thus  are  worse  than  useless. 

The  next  rule  which  an  interpreter  of  nature  should  bear  in 
mind,  is  not  to  attempt  too  much  at  first  ^  but  in  order  to  estab- 
lish a  sure  foundation  for  his  succeeding  labours,  he  ought  to  be 
content  with  obvious  and  unexceptionable  facts  ;  and  so  to  arrange 
these  facts,  as  to  lead  to  others.  To  elicit  novel  and  prominent 
facts,  is  the  lot  of  few ;  and  any  one  may  happen  to  be  so  success- 
ful. But  all,  as  before  stated,  may  investigate  truth  ;  and  thus 
contribute  more  or  less  towards  the  advancement  of  knowledgfe. 
Moreover  the  humblest  contributors  may  rest  assured,  that  they 
imperceptibly  raising  a  structure,  which  will  sooner  or  later  in- 
clude the  conspicuous  labours  of  their  more  fortunate  coadjutors  ; 
in  which  structure,  these  labours  will  indeed  still  appear  conspi- 
cuous ;  though  their  importance  will  be  diminished  as  the  fabric 
is  extended  around  them. 

The  remarks  just  made,  have  especial  reference  to  the  applica^ 
tion  of  chemistry  to  physiology.  The  cautious  and  judicious  ap- 
plication of  chemistry  to  physiology  has  already  effected  much, 
and  is  capable  of  effecting  still  more.  Indeed  it  is  hardly  possible 
to  say,  how  far  chemistry  may  extend  physiological  knowledge, 

25* 


294  CHEMISTRY  OF    ORGANIZATION. 

But  chemistry,  in  its  present  state,  in  order  to  be  made  really  use- 
ful, must'be  applied  in  a  manner  the  most  guarded  and  sparing- 
must,  indeed,  be  rigidly  confined  to  the  ascertainment  of  what  the 
living  principle  does  ;  and  how  it  operates  on  inorganic  princi- 
ples. With  the  living,  the  animative  properties  of  organized  bo- 
dies, chemistry  has  not  the  smallest  alliance  ;  and  probably  will 
never,  in  any  degree,  elucidate  these  properties.  The  phenomena 
of  life,  are  not,  even  remotely,  analogous  to  anything  we  know  in 
chemistry,  as  exhibited  among  inorganic  agents.  The  great  error 
of  chemists,  therefore,  has  been  their  attempting  to  apply  that 
science  to  explain  phenomena,  for  the  explanation  of  which,  che- 
mistry, as  we  have  said,  is  totally  valueless.  Such  perversion  of 
the  reasoning  powers,  has  too  much  prevailed  among  physiologists 
in  all  ages.  In  the  earlier  ages,  heat  was  considered  the  principle 
or  life.  In  later  times,  electricity  has  been  discovered  ;  and  to 
electricity,  the  same  functions  have  been  ascribed.  Life,  accord- 
ing to  other  philosophers,  is  motion.  But  the  progress  of  science 
has  dispelled  all  these  illusions  :  the  origin  of  the  obscure  and  eva- 
nescent principle  of  life,  must  be  sought  elsewhere.  By  heat,  for 
example,  many  wonderful  things  may  be  accomplished;  but  heat 
will  not  act  itself.  The  powers  of  electricity  are  still  more  won- 
derful than  those  of  heat :  but  electricity,  we  know  to  be  governed, 
in  its  mode  of  action,  by  certain  laws,  and  that  it  gives  no  sign  of 
intelligence.  In  the  same  manner,  life,  as  we  are  acquainted  with 
it,  cannot  exist  without  motion ;  but  motion  can  exist  without  life. 
Life  and  motion,  consequently,  are  not  synonymous  terms  ;  nor 
can  we  conceive  the  existence  of  motion,  without  a  mover.  In 
short,  the  living  principle,  as  already  pointed  out,  is  something 
difierent  from,  and  superadded  to  the  common  agencies  of  matter; 
over  which,  to  a  certain  extent,  it  has  a  control.  Thus,  the  phe- 
nomena exhibited  by  the  mysterious  agency  of  life,  are  strictly 
comparable  only  with  one  another  ;  and  have  no  relation  to  any 
inorganic  phenomena. 

But  the  desire  of  the  Physiologist  to  ascribe  to  the  agencies  of 
inorganic  matter,  those  operations  carried  on  wiiliin  living  bodies, 
is  merely  a  display  of  that  innate  propensity  of  the  human  mind, 
which  leads  us  to  seek  after  First  Causes.  The  conceptions  of 
the  physiologist  regarding  the  principle  of  life  are  the  same,  there- 
fore, as  the  conceptions  of  mankind  in  all  ages  regarding  the  Great 
First  Cause — the  Deity  himself.  The  poor  untutored  savage 
*'  sees  God  in  every  cloud,  and  hears  him  in  the  wind."  The 
complacent  philosopher  smiles  at  the  credulity  of  the  savage,  and 
perhaps  defies  "  the  laws  of  nature  !"  Both  are  alike  ignorant; 
nor  is  the  imagined  Supreme  Being  of  the  untaught  savage,  in  any 
degree,  more  absurd,  than  the  imagined  Pantheism  of  the  philo- 
sopher.    The  winds  we  know  can  be  referred  to  other  causes,  to 


CONCLUSION.  295 

which  they  are  immediately  owing  :  so  with  the  progress  of  know- 
ledge, the  "laws  of  nature,"  have  been  found  to  merge,  and  will 
continue  to  be  found  to  merge,  into  other  laws,  still  more  general ; 
thus  proving  that  these  laws  are,  all  alike,  mere  delegated  agencies. 
Hence  the  tendency  of  knowledge,  and  of  its  due  application,  is 
to  abstract  the  attention  from  inferior  things,  and  to  fix  the  mind 
on  the  source  of  all  knowledge  and  of  all  power — the  Great  First 
Cause  ;  who  exists  and  acts  throughout  the  universe ;  whom  we 
can  approach  only,  by  studying  His  works  ;  and  whose  works,  an 
eternity,  will  be  inadequate  to  explore. 


APPENDIX 


CONTAINING 


ADDITIONAL  NOTES  AND  EMENDATIONS. 


Page  33.  "  Forces  of  Gravitation." — Many  objections  have 
been  offered  to  the  term  vis  inertise  adopted  by  Newton.  In- 
deed, to  speak  of  mere  inertia,  or  inactivity,  as  a  force,  is  ob- 
viously absurd.  We  have  always  agreed  with  those  who  think 
that  the  term  inertia  has  been  unfortunately  chosen  ;  since  inertia 
expresses  only  one  quality,  as  it  were,  of  that  which  is  attracted, 
or  which  reacts,  in  nature.  But,  we  fully  acquiesce  in  the 
opinion,  that  whatever  resists  attraction  or  reacts,  is  as  appro- 
priately named  a  force,  in  a  certain  sense  of  that  term,  as  that 
which  attracts  or  acts  ;  and  such  resistance  is  in  all  instances, 
virtually  considered  as  a  force  by  the  mathematician,  however  he 
may  choose  to  designate  it. 

Page  42.  We  fear  the  terms  chemical  and  cohesive  axes  are 
not  quite  legitimate.  We  have  employed  these  and  other  familiar 
modes  of  expression,  such  as  ^^  forces  of  gravitation,"  "polar- 
izing forces,'^  &c.  above  alluded  to,  either  on  account  of  the 
general  reader,  for  whom  this  work  is  principally  intended,  or 
for  the  sake  of  analogy. 

Page  50. — Elementary  form  of  electrical  energies,  &c. 
Throughout  this  work,  as  just  observed,  we  have  adhered  as 
much  as  possible  to  the  common  language  ot  chemistry.  We 
conceive,  however,  that  chemical,  and  the  allied,  phenomena 
admit  of  being  expressed  in  terms  of  hypotheses,  of  which  the 
chief  are  the  following  : — 

1.  That  every  portion  of  matter  attracts,  and  is  attracted  by, 
every  other  portion  of  matter,  according  to  laws  which  have  ob- 
tained universal  assent. 

2.  That  all  matter,  as  it  is  known  to  us,  exists  in  the  condition 
of  molecules ;  which  molecules  we  consider  to  be  virtually 
spheres  or  spheroids. 

3.  That  all  the  spherical  or  spheroidal  molecules,  when  unim- 
peded, revolve  on  their  axes,  with  velocities,  which  in  molecules 
having  the  same  weight,  are  under  similar  circumstances,  fixed 
and   definite ;    but   which   velocities,   in  molecules  of  different 


298  APPENDIX. 

weights,  increase,  according  to  a  law  which  need  not  be  here 
specified,  as  the  weights  of  the  molecules  diminish. 

4.  That  the  molecules  of  the  imponderable  matters,,  liglit  and 
heat,  are  vastly  less  than  those  of  any  ponderable  substance  ; 
hence,  that  the  velocities  of  the  molecules  composing  these  im- 
ponderable matters,  are  inconceivably  rapid  ;  further,  that  the 
substance  of  these  molecules  is  either  fluid  or  elastic,  so  that 
they  become  more  or  less  oblate,  in  proportion  to  the  intensity 
of  their  motion. 

5.  That  the  imponderable  molecules  of  light  and  heat  obey  the 
same  laws  by  which  ponderable  matters  are  governed  ;  but  that 
these  imponderable  molecules  are  capable  of  pervading  and  ope- 
rating within  ponderable  molecules,  whose  motions  they  influ- 
ence by  the  intensity  of  their  own  motion;  and  that  the  mole- 
cules of  imponderable  matters  thus  appear  in  the  character  of 
agents. 

Page  64,  note. — The  term  "homogeneous"  light  is  a  mis- 
print :  we  mean  the  unaltered  light  of  the  sun.  Light  and  heat, 
and  indeed  all  self-repulsive  fluids  may  be  supposed  to  possess 
two  kinds  of  self-repulsive  power:  that  which  is  common  to 
them  as  fluids  ;  and  that  which  depends  upon  the  action  of  indi- 
vidual molecules  of  such  fluids  when  in  certain  positions,  and 
which  positions,  these  molecules  are  naturally  inclined  to  assume 
under  certain  circumstances,  particularly  when  in  motion.  Hence 
the  marshalling  of  the  individual  molecules  of  light,  supposed  in 
this  note,  probably  do  not  exist,  at  least  so  as  to  become  apparent, 
till  the  light  approaches,  or  passes  through  some  ponderable  me- 
dium. These  phenomena  of  light,  may  perhaps,  be  rendered 
more  intelligible,  by  what  appears  to  happen  with  respect  to 
gaseous  bodies.  The  rapidity  of  the  motion  of  gaseous  bodies, 
through  any  permeable  medium,  increases  as  their  specific  gravity 
diminishes.  Thus  the  force  with  which,  the  lightest  of  these 
bodies,  hydrogen,  struggles  to  escape  through  any  porous  matter, 
is  almost  incredible  ;  according  to  Mr.  Graham's  experiments, 
suflicient  to  raise  a  column  of  water  from  20  to  30  inches.  This 
rapidity  of  motion  seems  only  explicable  on  the  supposition,  that 
the  individual  molecules  of  the  gas,  in  their  passage  through  nar- 
row canals,  are  guarded  from  external  and  lateral  influence  ;  and 
are  thus  enabled  to  assume  that  position  which  is  natural  to  them, 
and  in  which  their  mutual  self-repulsion  is  the  greatest  possible. 
Hence,  a  single  row  of  self-repulsive  molecules  of  gas  (or  other 
self-repulsive  fluid)  passing  through  the  minute  apertures  of  a 
porous  vessel  into  a  vacuum,  or  what  is  analogous,  into  another 
gas  liaving  diflerent  self-repulsive  powers,  may  be  compared  to  a 
row  of  bullets  urged  by  an  elastic  fluid,  in  quick  succession 
through  a  gun  barrel :  but  with  this  difl'erence,  that  the  gaseous 


APPENDIX.  299 

molecules  propel  each  other ;  instead  of  being,  like  the  bullets, 
propelled  by  a  foreign  agency.  The  explanation  now  offered  of 
the  passage  of  the  molecules  of  a  gas  through  a  narrow  canal,  or 
through  any  porous  matter,  may,  as  we  have  said,  be  applied, 
not  only  to  the  passage  of  light  and  heat  through  various  media; 
but  also  to  the  passage  of  liquids  through  various  bodies,  by  the 
processes  which  have  been  termed  endosmose  and  exosmose. 
Do  these  forces  operate  also  in  capillary  attraction  ? 


300 


APPENDIX. 


Page  131 TABLE  OF  TEMPERATURES.— (from 


Isother- 
mal 

Zones. 


o 

o 

♦J 

o 

CO 


o 
o 

c 
o 


O 


o 
o 


ttl 

<y 
C 
o 


o 


Names  of  Places. 


Position. 


Latitude 
Nortli. 


Longitude. 


Height 
In  Feet. 


Nain       -     -     - 
*Enontekies  -     - 
Hospice  de  St.  ^ 
Gothard  -   5 
North  Cape 
*Uleo       -     -     - 
*Umeo      -     -     - 
*St.  Petersburg  - 
Drontheim  -     - 
Moscow      -     - 
Abo   -     -     -     - 


*Upsal      -     -  - 

^Stockholm  -  - 

Quebec  -     -  - 

Christiana    -  - 
^Convent  of  ? 

Peysenburg  3 
*Copenliagen 

*Kendal    -     -  - 

Malouine  Islands 

*  Prague    -     -  - 

Goltingen    -  - 

■'^Zurich     -     -  - 

'Edinburgh    -  - 

Warsaw       -  - 

*Coire       -     -  - 

Dublin    -     -  - 

Berne      -     -  - 

^Geneva  -     -  - 

^Manlieini     -  - 

Vienna    -     -  - 


57^ 

'  8' 

68 

30 

46 

30 

71 

0 

65 

3 

63 

50 

59 

56 

63 

24 

55 

45 

60 

27 

59 

51 

59 

20 

46 

41 

59 

55 

47 

47 

55 

41 

54 

17 

51 

25 

50 

5 

51 

32 

47 

22 

55 

57 

52 

14 

46 

50 

53 

21 

46 

5 

46 

12 

49 

29 

48 

12 

17 

18 
71 
10 

10 

12 
2 

59 

14 
9 
8 
3 

21 
9 
6 
7 
6 
8 

16 


Mean 
Tempe- 
rature 
of  the 
Year. 


61°20'w 

0 

20  47  E 

1356 

8  23  E 

6390 

25  50  E 

0 

25  26  E 

0 

20  16  E 

0 

30  19  E 

0 

10  22  E 

0 

37  32  E 

970 

22  18  E 

0 

38  E 

0 

3  E 

0 

10  w 

0 

48  E 

0 

34  E 

3066 

35  E 

0 

46  w 

0 

59  w 

0 

24  E 

0 

53  E 

456 

32  E 

1350 

10  w 

0 

2  E 

0 

30  E 

1876 

19  w 

0 

26  E 

1650 

8  E 

1080 

28  E 

432 

22  E 

420 

26.42° 
26.96 

30.38 

32.00 
35.08 
33.26 

38.84 
39.92 
40.10 

40.28 

42.80 
42.26 
41.74 
42.08 

42.98 

45.68 
46.22 
46.94 
49.46 
46.94 
47.84 
47.84 
48.56 
48.92 
49.10 
49.28 
49.28 
50.18 
50.54 


(*)  At  the  Places  thus  distinguished,  the  Ten^.peratures 


APPENDIX. 


301 


ENCYCLOPfEDIA  METROPOLITANA. — ARTICLE  METEOROLOGY.) 


given  are  the  result  of  at  least  8000  observations. 

26 


Maximum 

Distribution  of  Heat  in  the  different  Seasons. 

and 
Minimum. 

Mean  temp, 
of  Winter. 

Mean  temp. 

of  Spring. 

* 

Mean  temp, 
of  Summer. 

Mean  temp, 
of  Autumn. 

Mean  temp. 

of  warmest 

Month. 

Mean  temp. 

of  coldest 

Month. 

—0.60° 

23.90° 

48.38° 

33.44° 

51.80° 

—  11.28° 

+  0.68 

24.98 

54.86 

27.32 

59.54 

—0.58 

18.32 

26.42 

44.96 

31.82 

46.22 

+  15.08 

23.72 

29.66 

43.34 

32.08 

46.58 

22.10 

11.84 

27.14 

57.74 

35.96 

61.52 

7.70 

12.92 

33.80 

54.86 

33.44 

62.60 

11.48 

17.06 

38.12 

62.06 

38.66 

65.66 

8.60 

23.72 

35.24 

61.24 

40.10 

64.94 

19.58 

10.78 

44.06 

67.10 

38.30 

70.52 

6.08 

20.84 

38.30 

61.88 

40.64 

24.98 

39.38 

60.26 

42.80 

62.42 

22.46 

25.52 

38.30 

61.88 

43.16 

64.04 

22.82 

14.18 

38.84 

68.00 

46.04 

73.40 

13.81 

28.78 

39.02 

62.69 

41.18 

56.74 

28.41 

28.58 

42.08 

58.46 

42.98 

59.36 

30.20 

30.74 

41.18 

62.60 

48.38 

65.66 

27.14 

30.86 

45.14 

56.84 

46.22 

58.10 

34.88 

39.56 

46.58 

53.06 

48.46 

55.76 

37.40 

31.46 
30.38 

47.66 
44.24 

68  90 

^0  1ft 

VIO  *v7\J 

64.76 

tl  v  -  X  o 

48.74 

66.38 

29.66 

29.66 

4820 

64.04 

48.92 

65.66 

26.78 

38.66 

46.40 

58.28 

48.56 

59.36 

38.30 

28.76 

47.48 

69.08 

49.46 

70.34 

27.14 

32.36 

50.00 

63.32 

50.30 

64.58 

29.48 

39.20 

47.30 

59  54 

50.00 

61.16 

35.42 

32.00 

48.92 

66.56 

49.82 

67.28 

30.56 

34.70 

47.66 

64.94 

50.00 

66.56 

34.16 

38.80 

49.64 

67  10 

49.82 

68.72 

33.44 

32.72 

51.26 

69.26 

50.54 

70.52 

26.60 

302 


APPENDIX. 


TABLE  OF  TEMPERATURES. 


Isother- 

Posit 

ion. 

Mean 
Tempe- 

Names of  Places. 

Height 

rature  of 

Zones. 

Latitude. 

Longitude. 

the 
Year. 

in  feet 

*Clermont     -     - 

45°46' 

3° 

5'e 

1260 

50.00° 

*Buda       -     -     - 

47   29 

19 

lE 

494 

51.08 

o* 

Cambridge, (U.  S.) 

42  25 

71 

3  w 

0 

50.36 

05 

*Paris        -     -     - 

48  50 

2 

20  E 

222 

51.08 

O 

^London         -     - 

51   80 

0 

5  w 

0 

50.36 

o 
o 

Dunkirk       -     - 

51     2 

2 

22  E 

0 

50.54 

s 

o 

«J2 

Amsterdam  -     - 

52  22 

4 

50  E 

0 

51.62 

Brussels       -     - 

50  50 

4 

22  E 

0 

51.80 

09 

*Franeker      -     - 

52  36 

6 

22  E 

0 

51.80 

c 
o 

Philadelphia 

39  56 

75 

16  w 

0 

53.42 

N 

New  York 

40  40 

73 

58  w 

0 

53.78 

13 

'^Cincinnati    -     - 

39     6 

82 

40  w 

510 

53.78 

St.  Malo      -     - 

48  39 

2 

1  w 

0 

54.14 

o 

Nantes    -     -     - 

47   13 

1 

32  w 

0 

54.68 

1— < 

Pekin      -     -     - 

39  54 

116 

27  E 

0 

54.86 

*Milan      -     -     - 

45  28 

9 

11  E 

390 

55.76 

Bordeaux     -     - 

44  50 

0 

34  w 

0 

56.48 

a>  o 

Marseilles    -     - 

43   17 

5 

22  E 

0 

59.00 

Montpellier 

43  36 

3 

52  E 

0 

59.36 

2  o 

*Rome      -     -     - 

41   53 

12 

27  E 

0 

60.44 

1-  »o 

Toulon   -     -     - 

43     7 

5 

50  E 

0 

62.06 

Nangasacki 

32  45 

129 

55  E 

0 

60.80 

o  2 

*Natchez        -     - 

31   28 

90 

30  w 

180 

04.76 

*Funchal        -     - 

32  37 

16 

56  w 

0 

68.54 

^     CO    ^ 

Algiers  -      -     - 

36  48 

3 

1  E 

0 

69.98 

3  s 

*Cairo       -     -     . 

30     2 

31 

18e 

0 

72.32 

§-2  • 

^Vera  Cruz    -     - 

19   11 

96 

1  w 

0 

77.72 

*Havannah     -     - 

23   10 

82 

13w 

0 

78.08 

00     o 

^Cumana  -     -     - 

10  27 

65 

15  w 

0 

81.86 

At  the  places  thus  distinguished,  the  Temperatures 


APPENDIX. 

3US 

(continued.) 

1 

Maximum             1 

Distribution  of  Heat 

in  Different  Seasons.      | 

an 

d 

Minimum. 

Mean  temp. 

Mean  temp. 

Mean  temp. 

Mean  temp. 

Mean  temp. 
ofwarinest 

Mean  temp, 
of  coldest 

of  winter. 

of  spring. 

of  summer. 

of  autumn. 

Month. 

Month. 

34.52° 

50.54° 

64.40° 

51.26° 

60.20° 

28.04° 

33.98 

51.08 

70.52 

52.34 

71.60 

27.78  ■ 

33.98 

47.66 

70.70 

49.82 

72.86 

29.84 

38.66 

49.28 

64.58 

51.44 

65.30 

36.14 

39.56 

48.56 

63.14 

50.18 

64.40 

37.76 

38.48 

48.56 

64.04 

50.90 

64.76 

37.75 

36.86 

51.62 

65.84 

51.62 

66.92 

35.42 

36.68 

53.24 

66.20 

51.08 

67.28 

35.60 

36.68 

51.08 

67.28 

54.32 

69.08 

32.90 

32.18 

51.44 

73.94 

56.48 

77.00 

32.72 

29.84 

51.26 

79.16 

54.50 

80.78 

25.34 

32.90 

54.14 

72.86 

54.86 

74.30 

30.20 

42.26 

52.16 

66.02 

55.76 

66.92 

41.74 

40.46 

54.50 

68.54 

55.58 

70.52 

39.02 

26.42 

56.30 

82.58 

54.32 

84.38 

24.62 

36.32 

56.12 

73.04 

56.84 

74.66 

36.14 

42.08 

56.48 

70.88 

56.30 

73.04 

41.00 

45.50 

57.56 

72.50 

60.08 

74.66 

44.42 

44.06 

56.66 

75.74 

60.98 

78.08 

42.08 

45.86 

57.74 

75.20 

62.78 

77.00 

42.26 

48.38 

60.80 

75.02 

64.40 

77.00 

46.40 

39.38 

57.56 

82.94 

64.22 

86.90 

37.40 

48.56 

65.48 

79.16 

66.02 

79.70 

46.94 

64.40 

65.84 

72.50 

72.32 

75.56 

64.04 

61.52 

65.66 

80.24 

72.50 

82.76 

60.08 

58.46 

73.58 

85.10 

71.42 

85.82 

56.12 

71.96 

77.90 

81.50 

78.62 

81.86 

71.06 

71.24 

78.98 

83.30 

78.98 

83.84 

69.98 

80.24 

83.66 

82.04 

80.24 

84.38 

79.16 

■ 

o-iven  are  the  result  of  at  least  8000  observations. 


304  APPENDIX. 

Page  163,  Note. — We  have  stated  that  the  diffusion  of  the 
same  air,  and  of  the  same  vapour  at  different  temperatures,  are 
inferences  only  from  the  supposed  general  law  of  the  diffusion  of 
gaseous  bodies;  and  have  alluded  to  the  existence  of  modifica- 
tions of  that  general  law.  To  those  who  feel  an  interest  in  such 
inquiries,  the  following  additional  remarks  may  be  not  unaccepta- 
ble, as  pointing  out  the  grounds  from  which  we  infer  such  diffu- 
sion of  the  same  air  and  vapour  ;  and  the  modifications,  to  which 
we  have  no  doubt,  it  will  be  found  to  be  liable. 

Let  us  suppose  a  flexible  air-tight  bag  to  be  furnished  with  a 
stop-cock  ;  and  to  be  filled  with  hydrogen  gas,  under  exactly 
the  same  pressure,  and  having  the  same  temperature  as  the  sur- 
rounding atmosphere.  Let  us  now  suppose  the  stop-cock  to  be 
opened.  Lumediately,  the  hydrogen  in  the  bag,  and  the  exterior 
atmospheric  air,  will  begin  to  commingle,  with  a  force  and  velo- 
city proportional  to  the  quantity  of  the  gas  diffused  ;  and  which 
quantity  varies  inversely  as  the  square  roots  of  the  specific  gravi- 
ties of  hydrogen  gas,  and  of  atmospheric  air  ;  that  is  to  say,  the 
volume  of  atmospheric  air  diffused  inwards,  being  supposed  to  be 
equal  to  J,  the  volume  of  hydrogen  diffused  outwards,  will  be 
equal  to  3.8  nearly.  The  diffusion  of  hydrogen  and  atmospheric 
air  of  the  same  temperature,  and  under  the  same  pressure,  is  an 
instance  of  the  simplest  form  of  gaseous  diffusion  ;  and  is,  we 
believe,  the  only  form  of  diffusion,  which  has  been  experimentally 
investigated.  The  phenomena  attending  the  diffusion  of  these 
two  bodies  show,  that,  all  other  circumstances  being  supposed  to 
be  alike,  the  diffusion  of  gases  is  influenced  solely  by  the  differ- 
ence of  their  specific  gravities. 

We  have  stated  the  case  of  the  diffusion  of  two  gaseous  bodies 
having  the  same  temperature.  Their  temperature  however,  may 
vary  within  any  limits  ;  and  though  the  law  of  diffusion  may  be 
modified,  diffusion  will  continue  to  take  place,  (except  at  those  tem- 
peratures at  which  the  specific  gravities  of  the  two  gases  become 
equal,  at  which  temperatures  there  will  be  no  tendency  to  diffu- 
sion) ;  provided  difference  of  specific  gravity  alone  be  the  cause 
of  diffusion.  But  if  the  diflusion  of  diflerent  gases  at  different 
temperatures  be  admitted,  it  seems  to  follow,  that  different  por- 
tions of  the  same  gaseous  body  under  the  same  pressure,  but 
having  different  temperatures,  and  consequently  different  specific 
gravities,  will  likewise  have  a  tendency  to  diffusion. 

The  case  we  shall  next  suppose  is  dissimilar  to  the  two  fore- 
going cases,  but  is  deducible  from  the  same  premises  ;  it  is  the 
case  of  the  diffusion  of  the  same  vapour,  as  of  the  vapour  of  water, 
which  may  be  illustrated  in  the  following  manner: 

Let  us  suppose  our  apparatus  to  contain  atmospheric  air, 
having  the  temperature  of  100°,  and  saturated  with  water;  while 


APPENDIX.  305 

the  exterior  atmospheric  air  is  at  the  temperature  of  60°,  and  is 
likewise  saturated  with  water  ;  and  that  the  pressure  on  the  air 
confined  in  the  bag,  is  the  same  as  the  external  pressure.  We 
suppose  the  presence  of  air  in  the  apparatus,  in  order  that  it  may 
be  able  to  sustain  the  atmospheric  pressure ;  for,  as  we  formerly 
stated,  vapour  alone,  at  ordinary  temperatures,  exerts  elastic  forces 
very  different  from,  and  far  inferior  to  the  elastic  force  of  air  at 
these  temperatures.  Such  being  supposed  to  be  the  state  of  the 
air  contained  in  our  apparatus,  what  will  happen  on  the  opening 
of  the  stop-cock  ?  The  air  within  the  bag  will  have  the  same 
tendency  to  diffusion,  as  the  contents  of  the  bag  supposed  in  the 
last  case ;  but  the  vapour  with  which  the  air  is  associated  will  have 
an  opposite  tendency.  The  warmer  vapour  within  the  apparatus, 
instead  of  being,  like  the  warmer  air,  lighter;  will  have  a  greater 
specific  gravity  than  the  colder  vapour  associated  with  the  ex- 
ternal air.  Consequently,  the  inv/ard  tendency  to  diffusion, 
that  is  to  say,  the  tendency  of  the  colder  vapour  without  the 
apparatus,  to  diffuse  itself  among  the  molecules  of  the  warmer 
vapour  within  will  be  greater  than  the  outward  diffusive  ten- 
dency of  the  vapour  in  the  apparatus.  Such  will  be  the  op- 
posing diffusive  tendencies  of  warm  vapour  and  of  warm  air  in 
a  state  of  commixture;  and  if  the  air  were  absent,  the  diffusive 
tendency  of  vapour  alone  would  have  a  similar  diffusive  tendency 
to  that  which  it  has,  when  mixed  with  air ;  though  that  tendency 
would,  of  coarse,  be  not  exactly  the  same  as  when  modified  by 
the  influence  of  the  air.  The  vapour  within,  and  the  vapour 
without  the  apparatus,  would  each  exert  the  elastic  forces  peculiar 
to  their  respective  temperatures  as  vapour. 

There  would,  however,  be  a  striking  difference  between  the 
phenomena  attending  the  diffusion  of  vapour,  (whether  mixed  or 
unmixed  with  air),  and  that  of  air  itself  at  different  temperatures. 
Two  portions  of  air  at  different  temperatures  would  cease  to  have 
any  diffusive  tendencies  as  soon  as  their  temperatures  became 
uniform.  The  temperature  of  two  portions  of  vapour  becoming 
uniform,  would,  of  course,  produce,  in  the  same  manner,  a  cessa- 
tion of  their  diffusive  tendencies  ;  but  the  circumstances  accompa- 
nying that  cessation  would  be  altogether  different.  The  colder 
vapour  v/ithout  the  apparatus,  being  the  lighter,  would  move  with 
accelerated  velocity  into,  or  toward,  the  heavier  warm  vapour 
within  the  apparatus  ;  while  that  warm  vapour,  in  moving  out- 
ward, would  be  instantly  condensed ;  and  thus  its  diffusive  pow- 
ers would  be  annihilated.  On  these  grounds  we  advanced  the 
opinion,  that  probably,  there  may,  under  certain  circumstances, 
exist  in  the  atmosphere,  a  tendency  to  diffusion  from  above  down- 
wards ;  the  vapour  in  the  higher  regions  of  the  atmosphere,  being 
relatively  lighter  than  the  vapour  below. 


306  APPENDIX. 

The  observations  that  have  been  offered  in  this  note,  regard  the 
only  circumstance  which  is  yet  known  to  cause  a  difference  in 
this  diffusive  tendency  of  gaseous  bodies,  namely,  the  difference 
of  their  specific  gravities.  If  there  be  other  causes  of  such  differ- 
ence ;  and  it  is  ahnost  certain  that  there  is  one  other  cause  ;  the 
effects  produced  by  these  causes  may  be  very  different.  The  dif- 
ference in  the  diffusive  power  of  the  same  gaseous  body,  is  not 
perliaps,  under  any  circumstances,  very  remarkable  ;  but  there 
will  probably  be  found  to  be  a  much  greater  difference  in  the  dif- 
fusive power  of  vapours  ;  though  it  is  not  easy  to  form  even  a 
conjecture  as  to  the  extent  of  that  difference.  In  the  present  state 
of  uncertainty  therefore  on  those  points,  we  have  thought  it  right 
to  speak  of  a  tendency  to  diffusion,  rather  than  of  diffusion,  as  a 
thing  actually  existing.  The  diffusive  powers  of  elastic  fluids 
are  at  present  very  little  understood  or  appreciated.  They  con- 
stitute, however,  as  we  have  said,  one  of  the  most  interesting  and 
important  subjects  in  physics,  and  would  amply  repay  whoever 
would  take  the  trouble  to  investigate  them. 

Page  207. — The  table  follows,  illustrating  the  distribution  of 
plants  over  the  globe,  to  which  we  have  referred  in  the  text. 
It  has  been  copied  immediately  from  Lindiey's  Introduction  to 
Botany. 


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